Can the "kill 400 minions as a team" VS. mission be completed in a custom game...?

...with players on opposing teams? You do earn IP for those games, and the quest text doesn't specify that it must be a "matchmade" game. Anybody have any clarification on this? Or just tips in general for getting this?

EDIT: the mission is called "Chaotic Alliance." Not sure what the Order version of the same mission is called.