I just purchased the GoG version and it installs as 5.17(481), I also have the GamesGate version but cannot comment about updating as I have never installed it. (probably wont now)
It has some gog.* extra files compared to a GamersGate release but still has the update.cmd for patching. Thought I would check that as GoG always use their own custom patches.
Hope they get some of the Gravitea later games as well. I would buy Operation Star again if GoG got it. But sure if GoG would host the normal Graviteam patches as they would probably not be compatable with their new client.
I would love to see any new Graviteam games at GoG, that would be very good.
Regards MarkL