I have now three versions (build 1008, build 1028, Steam version) and I can run all three of them. Yesterday I did some practice for todays race in build 1008 version multiplayer mode while having the Steam version installed. The only inconvenience is that I have to sign in on my rF2 account (in the Launcher) every time I switch from Steam to non-Steam versions. See this posting:
rFactor 2 launches on Steam with a hefty discount
So, having the Steam version installed should hopefully not be an issue regarding participating in todays race.
Or is it something I've missed?