I am not sure but if someone made a custom skin, nobody could see it in multiplayer unless the server had the skin and assigned it to a plane. (you can't even fly it in multiplayer as far as I know)
When I was playing IL-2 in multiplayer someone could have made a skin for his own, and flown around in it while else nobody had it. but after a while in the server, the skin downloaded to all the clients in the server and everyone could see the beautiful skin he had on his plane.
the skin would have downloaded to a cache folder inside the game. you could look back for it, copy it and place it with your own skins.
In IL-2 it was simple: Pick a plane (out of the extensive list unless in coop), chose nation and skin, FLY.
If you ask me DCS and LOMAC do things way to complicated.