It struck me a while back that it’s likely not so much that Trump lies per se as that his brain is broken in such a way that he just doesn’t distinguish between truth and falsehood. To him, that’s a meaningless concept. He just says, and means, whatever he says at the moment, based entirely on how it might serve his interests to say it.
He measures value in other people differently - primarily based on their loyalty to him. But again, the part of his brain that distinguishes between truth and falsehood is broken, so all that takes is a profession of loyalty. And as far as that goes, Vance is particularly notable, since he has in the past criticized Trump, but is now sucking up to him. I think that to Trump, in his narcissism, that’s especially appealing because it means that he won him over.
So then it’s not so much that he expects Vance to lie as that he expects Vance to remain loyal. It’s not so much that he sees integrity as an obstacle and the lack thereof as an advantage as that he sees it as a threat to loyalty and its absence as an aid to loyalty.
All of that also explains how it is that Trump - an inveterate liar and back-stabber - is so willing to trust people and so bitter and petulant when they turn against him. Since he doesn’t distinguish between truth and falsehood, he doesn’t see the expectation that they lie on his behalf as anything unusual, nor does he recognize the likelihood that they’ll one day want to or be coerced to stop lying and tell the truth instead. To him, it’s just a simple question of whether they’ll remain loyal to him by saying what he wants them to say (with no understanding of the relevance of the fact that it’s a lie) or betray him by saying what his opponents want them to say (similarly with no understanding of the relevance of the fact that it’s the truth).
So in Vance, he sees someone that he won over to his side, and his lack of integrity as a lack of that misplaced loyalty that’s led others (Pence, for example) to, as he sees it, betray him.