I haven't tested this but I think that if you oorah before the MG fires, you don't get suppresed by the MG.
This is actually a problem.
It would be if you are right. It would require more thorough testing to prove right or wrong.
In my experience this is not the case. But judging from play experience isn't enough because it can be hard to tell in the heat of the battle when the first round was fired.
I know for sure that cons doing oorah can be supressed, but if it depends on the time it was activated, I don't kknow.
Wrt. AP, I don't find it very usefull, because how often do you make it to vet 1 by the time M3s appear? That's gotta be very rare. Even by T70-time it must be hard.