They probably can for the purposes of the TCPA, as they establish a contested issue of material fact. They're not terribly useful in the actual trial phase unless someone shows up, though.We don't even know if the affidavits can be admissible as evidence. Probative value has to exceed prejudicial value and so on. And if it's a "I heard from a friend who saw another friend get RAPED by Vic," that's probably not admissible, either.
It's looking like the TCPA phase is going to be a battle of the affidavits, but I don't see how the defense knocks out a defamation case based on the mere fact they can establish that they actually have an affirmative defense. A jury has to decide that.
So it seems like there are a couple hurdles here, the less-discussed TRCP 91A special exceptions that are getting a hearing, a probable TCPA, which looks like it's shaping up to be somewhat like a summary judgment motion, and then, possibly, another actual summary judgment motion after discovery. As well as any interlocutory appeals if anyone wants to try their luck at that after losing a TCPA.