Sure they do, quite a bit. Especially on recreational profiles. I dive all the time (Rec profiles) with a UTD guy in his UTD sidemount rig. He also recently chose to take Fundies in back mounted doubles, eyeing GUE Tec 1.
But, as a newish Tec1 diver, I choose to only be a team mate with GUE for technical dives due to my own newbyness. That means, at a minimum, there is one other GUE Tec diver specifically teamed with me. Often there are other agency divers with us, in their own teams. This is not a GUE directive, it is the choice I've made.
The great thing about GUE is that you can be anywhere in the world, jump into a team, and everyone is on the same page immediately. This benefit can not be overstated.
But, as a newish Tec1 diver, I choose to only be a team mate with GUE for technical dives due to my own newbyness. That means, at a minimum, there is one other GUE Tec diver specifically teamed with me. Often there are other agency divers with us, in their own teams. This is not a GUE directive, it is the choice I've made.
The great thing about GUE is that you can be anywhere in the world, jump into a team, and everyone is on the same page immediately. This benefit can not be overstated.