This may belong in the rules section, but since it only pertains to Marines, I thought to put it here instead.
Simple enough question though. If an enemy unit is within 6" of a SM unit that broke, would the SM Unit automatically regroup due to the ATSKNF rule?
My stance on this is that they will regroup. In the codex it is very explicit in stating that they will "ALWAYS" regroup. I checked in the rule book about the regrouping rules and the unit within 6" thing, and it only says that a unit is not allowed to "roll to regroup" if an enemy unit is within 6". With the ATSKNF rule, there is no rolling involved. Since the other rules affecting the rolling regroup do not apply to Marines, then this shouldn't prevent them from regrouping either.