chaos and chaos dwarves are two seperate armies with seperate books and background, etc, etc.
So unless it was a friendly game where the rules were bent/broken - no, the hellcannon cannot be used in CD army. Just like you can't use a great cannon in a dark Elf army.
Hi Xan,Ravening Hordes is still legal (as the list for Chaos Dwarfs) as GW has not yet contested it or listed otherwise. GW clearly stated that RH will remain until it is superceded.