Pretty much what Paton said. While you can have multiple mouse keyboards active, the problem is the system will not know which is for use with the main system and which is for use with the VM. So mv 1 or the other will affect both.
Plus in addition to that, the VM will have bad graphics, so bad you might not be able to play BF3. In addition to the fact you would need 2 copies of the game to play.