I brought this up earlier in the Extermination thread.
At first look, it does, but you have to see that "successfully campaigned beside without incident" and "lingering resentment and malcontent bordering on internecine strife" are not mutually exclusive.
For example, they could have fought together while hating each other's guts. This hate could bubble up into almost physical violence...but never did quite hit the boiling point.
At the end of the day, the mission is accomplished, no incidents happened, but they can still hate each other. Or at least the Iron Hands can hate the Alpha Legion.
