I have no idea. But I reckon this is probably best in the 40k fluff forum

 

Strait up most eldar hate humans and consider them nothing but primitive barbarians. Not people to be allies with but tools for thier own intentions. The only real eldar I know of to have anything to say about the emperor is eldrad and he thinks that the emperor is a short sighted fool who was warned about the downfall of man and the batrayal of the mariens, but he didnt listen. look what happened. people who dont listen to Eldrad/eldar in general get what they deserve.

How do they reconcile their own assumed superiority in the face of the 'miracles' that are constantly (and sometimes, falsely) contributed to him?

The emperors "miracles" are but a small fraction of what the eldar race were capable of in thier prime. planets brought to life and stars dieing and all that stuff. They are probably unimpressed with him as a whole, but very impressed of his capabilities for just being a human.

 

I beleive that the Eldar would hate the Emperor as they would an enemy. Seeing as he was selling his race off to the Chaos Gods in a bid for power. Most anti-chaos armies would probably beat the leaving crap out of him.
As for his miracles- they were either warpspawned or technological (the latter far outnumbering the former). Considering what the eldar can do technologically and considering what their magic is capable of, they probably look at his technology like a beaten-down 80's buick next to a Formula 1 car, and view his magic as very dangerous parlor tricks.
The emperor has no reason NOT to live harmoniously with the eldar, they never offended or slighted him and have often come to save human's butts. The eldar would surely not accept humans as 'equals' within the standards of relations, but as martial allies I could definently see a strong alliance being formed. IF humans weren't xenocidal...

 

Eldrad apparently didn't like him, as he claimed to have tried to warn the Emperor of the Horus Heresy (note: he claimed to have done so) only to have the Emperor ignore him. Eldrad concluded that the Emperor, like all humans, was powerful enough to be regarded as a threat but too stubborn, arrogant and generally stupid to really replace the Eldar.

Of course, Eldrad's dead, so...I don't know if you want to take his word on that. But generally the Eldar think the Emperor was

a) powerful.
b) stupid.

 

...which is how they view the Imperium in general.

The Eldar likely are too busy viewing the Emperor (and by extension humanity) as an upstart group of monkeys to really recognize where he stands.

The Emperor is despised violently by the chaos gods, partially because of his Great Work, with the Grey Knights.

The eldar boast no similar psykers who are both powerful physically, mentally and a blinding anathema to the forces of chaos.

As to humanity's xenocidal tendancies... This ain't star trek. The humans on most alien conquered worlds were enslaved, twisted, or being used as food stock.

 

At the time of the Crusade, Eldar were still a bunch of refugees, and probably a bit busy with their own problems to do much pondering about what the ugly little vermin were up to.

As poodle said, the few Eldar quotes on the Emperor seem to read either 'irrelevant' or 'powerful enough to be dangerous, stupid enough to get himself killed.'

At the end of the day, vermin is still vermin.. The eldar may not be actively hostile all the time, but they're not remotely friendly with humans any more than I'd be friends with a rabid dog.. I might occasionally direct the dog at other people, but as soon as it gets out of control.. Well.. you've seen 'Old Yeller.'

 

Just like many have stated, Eldar never seldom engage in diplomatic missions and the such to hold some form of agreement with the Imperium of Man. Most leaders and farseers would tend to rally with a group of humans if the hour was dire and action was needed (like for instance, stopping a daemonic summoning or a necron crypt from activating, etc. etc.) simply because Eldar rely on being subtle and manipulative, sometimes treacherous...

The only xeno race that actively engages with representatives of the Imperium on some planets are the Tau, reprsented by their Water caste emissaries, and there again, humans show signs of xenophobia. A common example of this fact would be in the Ciaphas Cain series of books, when our ever-so-faithful (tch... yeah right... XD) commissar lands on Gravalax when the situation is so tense battlesuits and chimeras are crawling around the cityscape...

Coming back to the main question about the Eldar, I'd suspect some craftworlds could come to some form of mutual "agreements" with local representatives of the Imperium, although it would never go to a point where both races would form a strong alliance, much like the Empire and Dwarfs in Warhammer Fantasy. Even so, some Eldar factions, most notably craftworld Biel-Tan, would be most reluctant to give any non-eldar such a level of trust... more likely at the tip of their starcannons and bright lances heh...

 

Have you read the newest Horus Heresy book, Fulgrim? It paints an interesting picture of how Eldrad and the Eldar of Ulthwe were during the Crusade. None of them really trusted the humans but Eldrad believed that he saw something in Fulgrim, perhaps seeing his appreciation of life and beauty and seeing in him a chance for humanity's salvation. The fact that he didn't order the Eldar Maiden Worlds within the Perdus Rift burned without a second thought would seem to have indicated that, until Eldrad saw Fulgrim carrying a daemon weapon. The resulting battle was an experience that forever changed his perspective on the universe. Perhaps once, he was willing to give humanity a chance but no longer.