More MSQ Stuff
I don't think the white-robed figure talking to Zenos can be Venat. The figure says his knowledge of the Final Days of Amarot is mostly second-hand. That really doesn't match up with Venat being around for Zodiark's summoning which was in the Last Days. I also have a hard time seeing Hydaelyn's summoner referring to that time period as "the world's end" since the entire point of Hydaelyn was to keep the world from not ending.

If I had to take a guess who Venat ended up becoming, I'd say Minfillia is a way better guess. Minfillia is repeatedly said to have been the most attuned to Hydaelyn's thoughts and voice out of all the Echo users and Minfilia literally became Hydaeyn's voice. She directly calls herself Hydaelyn's Emissary at one point even. She's very much a counterpart to Elidibus in that both of them claim to speak for their various gods instead of themselves.

It's worth noting that while the 14th Convocation member wasn't a part of Hydaelyn's summoning initially, there's nothing preventing them from joining her side later. Which could actually be more evidence for the 14th Convocation member being tempered by Hydaeyn. If they didn't die while summoning her, then I can't think of any reason she wouldn't be able to temper them same as Zoidark did to the Ascians if she wanted to.