Tamme's on the waiver wire, I'd pick him up and roll with whichever Broncos' TE plays.
TE is just one big ass dartboard anyway, so roll with the one that has Peyton Manning throwing the darts
Your thought process is correct, but Denver isn't using Tamme much when JT is out. He played like 40% of the snaps last week with one target. Denver actually started Virgin Green, blocking TE, last week in Thomas' absence.
Fleener on the other hand has a tasty matchup against a team in disarray, a QB who loves to target him and opportunity with Allen out.
I'd say it goes like this:
1.) Thomas- if he plays he is the best bet, but he hasn't practiced so you have a less than (made up number time) 40% chance or so that he plays
2.) Fleener- safest play by far. Put him in now and expect at least 8-12 points with TD potential
3.) Tamme- you roll the dice on Thomas, who sits, and now you are stuck with Tamme who does nothing
so you go boom or bust or you just play it safe with Fleener. Easy call. If say a guy like Jace Amaro were available (he is, but he isn't playing MNF w/ concussion) you might roll the dice on Thomas because you have a less dicey backup plan... but as it stands, Tamme being the only safety net.. you gotta go Fleener.