You are able to duplicate any item that is capable of fitting into a your uniform or vest using the inventory of a vehicle. Once the item has been duplicated the game does have some knowledge of it being a duplicate because you cannot place the duplicated item into one of your player's containers if the original or another duplicated item is present already. This can be seen in the linked video, as well as not being able to throw the duplicated grenade. However, duplicated magazines are still usable and using script commands such as "weapons player" and "magazines player" include the duplicated item, so if a mission has persistence, a quick "soft log" will result in the duplicated items behaving as normal items.

I have unfortunately not been able to test this in multiplayer but will attempt to tonight and see if another player is able to pick up the duplicated item.

Modded content that doesn't restrict what items can be placed into vests allow for this to be used on primary weapons as well.

This was tested on both 1.52 and 1.54.133353 (RC Branch).