I wouldn't think it would be functional in the normal way.
1) You shouldn't need to give any forward assist to a paintball.
2) Things may get messy if you did.
I agree it'd be nice if it did something, but given the statements that this is focused towards military folks as well, I can see where you'd need that there. Part of qualifying with your rifle is learning FTF procedures and slapping the forward assist is part of the routine. Besides just going for realism, that could explain why it's there.