Return of Reckoning

Is there any rule that I would break by adding the game to steam? or could I get red flagged for something by doing so?

I just did (I'm used to open games from there and I was hoping my friendlist get to see what I'm playing) and got a message that the server closed my connection. Before I get flagged I want to know.

You mean as a non-steam game? Then yes that is fine.