I've posted this before elsewhere in a similar thread.
All members of the lobby would need to have the DLC in order for the gun model to be available for other players to pickup when dropped.
The same goes for map DLC - you can't play the maps if one person in the lobby doesn't have it
Ok can we get something clear, here are my thoughts and your wrong about everyone have to have the gun.
When you order Collection One, it be in its own playlist just like nuketown 24/7 is, So anyone with the Collection One will play within that list, if you don't have the Collection One you won't be able to play in it, and that means they can implement the gun into the game, cuase the players wihtout the Collection One will be Playing the Core Game Types, So why can't they put a new gun into the game, if you don't buy it you won't be playing the play list anyways,
Know I know what if you don't buy Collection 1 and you only buy the other's, well I'm sure that all the Dlc will be in one big playlist buy itself, and if you don't have any of the DLC only one, you only get match up with the DLC you have, so there you won't have to ask that question, so yes they can put a gun into MP and seperate it from the ones that don't have it, so I really think this GUN is for Zombie's cause of the name PeaceKeeper.