They are installed in separate directories so you should be fine.
I really don't use Steam right now. I went ahead and installed the GOG version and it wrote over the game game saves from Steam version. Fortunately I had backed the folder up and copied it back and all my saved games were there. Whew!
I will say that the GOG version is much nicer; at least graphics-wise on my MAC.
Again...thank you for taking the time to respond.