I think it's definitely not beyond the realm of possibility. The thing is that Rousey seems a horrible match up for Tate. Stopped her twice. In fight 2 she dominated her- absolutely schooled her on the ground and tossed her left and right.
The thing is though that Tate's hands are clearly, clearly better than Ronda's in my opinion. She was landing some hard shots in Ronda in their second fight though they were of course of minor importance since Ronda had such a major advantage over her in the grappling and since Tate played right into that advantage by foolishly clinging to the strategy of shooting in even though Ronda had her so well scouted and could gain the upper hand with her judo each and every time.
If Tate fought smart in the third fight, I think she could definitely give Ronda problems and potentially hurt her standing.