I see your point but I'm just not sure it increases his odds, since I think he will have to earn his spot, either way. The catcher signings do serve as insurance to make sure Rochester has options at catcher, assuming Mitch does make the Twins out of ST. I expect that he will, but it's not like they'll say, "well we HAVE to keep Garver in Minn b/c we have these other guys at Rochester and don't have room for him down there."
Well, because he is on the 40-man, Garver would be the catcher of choice at the moment. The question is will he get enough playing time behind-the-plate. Garver will be given every chance to break camp, as a bench player. If he can produce with the bat, than the question comes do they use him as a bat and in the field more often than not, and a third catcher on the roster would then be a necessity.
The Twins have no catchers at Rochester. Look for them to sign at least one more backstop, as your Chattanooga choices include Brian Olson and Brian Navarreto. The Twins will want some depth to choose from (who remembers them signing Eddy Rodriguez last season) and they do need to break camp with at least a viable option at AAA that could hold a 40-man spot for the season and not risk loss everytime they send him up and down.
More names will happen. The Twins, by my calculation, signed around 36 minor league free agents alst season. Might be something of a record, especially considering how many of them did see 40-man roster time on the pitching staff.