I wouldn't put it past them, all celebrities care about these days is the money. And vaping to make money sounds like a very easy task, I would do it!
There is no telling what these celebrities are getting paid to do these days. I dont now if it would be to vape though.
If celebrities are getting paid to promote products on Twitter, it wouldn't surprise me if they were being paid to be seen using products like an e-cigarrette. These kinds of deals aren't always made public though, as it makes the advertising approach less effective.