With the recently announced New Jedi Order movie, there's always a chance he comes back there, assuming he survives past the Mando-verse stuff.
The episode was called Spies. They've been pretty intentional on their word choices this season in the titles. That would indicate more than one.
As far as the possible Mando spy, three possible candidates: Axe Wolves, The Armorer, or the surface survivors.
The similarity of The Armorer's and Gideon's armor, her abrupt change in attitude toward Bo on Nevarro and now being gung ho to get them to go to Mandalore, and taking off before the battle makes her suspicious.
Axe Wolves going to get "help" during the battle makes little sense as who was he going to get help from? The only ship they landed with (one of those dumb tactical points things that I previously mentioned) left the surface and you supposedly cannot contact space from the ground. Plus pretty sure all of the away team was already there. Still probably hates Bo after losing command, but not sure when he had time before this to get on Gideon's payroll.
The survivors conveniently know about the forge, but not the secret Imperial base just 10 feet away? Seems suspect They are easiest to believe, but nothing they did outside of bringing the away team to the forge faster really screams spies. Then again, they level of subtlety of this series is sometimes lacking.