While it's beyond doubt that the (False) Griffin's opinion of Zenos is heavily biased, his word is all we have about Zenos so far... and as you know, it's not flattering at all. I'm not the type to judge a person as good or bad before getting to know them, though, and whatever plans Zenos has yet remain completely in the dark. We've only gotten the barest glimpse of him in-game, in the 3.5 trailer!

... that said, just because he's the Legatus of the XIIth Legion doesn't mean he'll be an analogue to a major character or antagonist from XII. We don't know if Regula is going to be an analogue to a VI character, though that's widely speculated to be the case. While Nael had some conspicuous similarities to Sephiroth, aside from being on a floating continent with the Warring Triad we don't really have any major similarities between Regula and any VI character that I know of. Yet. That could change in 3.5 but until we know it is... going to... err...

It could be that Zenos is actually a good person pretending to be a tyrant so once he's made Emperor he can reform the Empire and liberate all the conquered territories. Perhaps he knows about the Ascians and is working on some complex scheme to free history from their reins what requires him to be a douche until he pulls it off. Or perhaps he really is just an iron-heeled tyrant and the XIIth Legion is just representative of the moral ambiguity surrounding the Resistance factions and revolution in general. Time will tell.