It looks like the reinfotcement EXO is a wildcard while the deployed one isn't. Am I right in assuming that means he can't join an exrah link team, or anything really.
You are right. Troopers from the Main Section cannot be part of the Reinf. Fireteams of the Reinforcements Section. In the same way, Troopers from the Reinforcements Section cannot be part of the Fireteams of the Main Section.