Sorry it's been a while before anyone replied. The forum has been giving me database errors most of the time, I try to reply to your post every so often and finally tonight it's let me!
I've never had a problem combining wethers and tups. I usually run them alongside each other for a few days, then open the gate. Obviously, if there was any aggression at the fence line then yes, one would use the same tactics as combining tups.