SourceOP won't work on gmod10. If they have linux binaries, I will see what I can do to make it work, but until then I really can't.

The SourceOP thing in the game description that you are talking about is off by default. This is because it causes issues with some other plugins (I guess they read from the game description). If you want to turn it on, you need to set the DF_modify_gamedescription CVAR to 1. For a full list of CVARs please see: http://www.sourceop.com/wiki/Server_CVARs .

In css, the rank and credits do not display because they have disabled hud messages. There may be a workaround to this, but I haven't done much investigation.