Don't you think we would've heard of Vega's unblockable by now? Come on.What I found that Vega will always cross up if you go under him in his start up. So Vega has an unblockable. But what I don't get is why the first part of the move is not considered a cross up.
Here's what I got recreating it in training.
I got two block effects in the replay for some reason.
And while I crouch after the first hit, It doesn't count as a cross up after that.
And you can't really tell anything from these screenshots. Doesn't look like your last input was blocking high, but it's too chaotic to really tell.