Not sure, Clone Carnage doesn't really have an online player roster in general. While steam users can use online play, you can't find a server most the time to play on.
For now, I am under the assumption that there is no online play with GOG due to lack of mention of online multiplayer in product description and many other problems. I expect this game to never get online multiplayer.
GOG isn't popular in the mainstream and a lot of people that use gog share accounts. Also GOG being DRM-FREE makes it hard for game devs like to implement secure online multiplayer.