Melusca on the Steam forums helped me resolve this issue. If you are experiencing issues with the Steam UI option not appearing in game try creating a new character. Then while playing under the new character hit ESC and try to change the Interface option to the Steam UI under that character. I found the Steam UI option reappeared under the new character. Once set save and exit the game then restart the game. When the game loads back up you should have the Steam UI working both in the Main Menu as well as on your old character saves.