I tested the results on server with reunion (0.1.0.135) and dproto (0.9.582)
Results were, I was able to connect on dproto but not on reunion server giving message: your steam id is already in use on this server
Seems like its something related to Reunion, I had a look into cvars and configs of reunion and dproto but wasn't able to figure it out.
If there is no present solution to it, I think it should be added in config and server owners can enable or disable this feature [With Defined Max Limit], since after steam family sharing, there is probability of 2 users playing with same steam id (what I read on internet).
Edit: I just came to know, regarding Steam Sharing, Yes steam ids are same but only one user can play/share library/cs1.6 at same time, even with different pc's.