is reagent a wrapper for a specific version of react, or can it be used with any react version?

Reagent has to be manually updated to handle new versions of react. See the reagent changelog: https://github.com/reagent-project/reagent/blob/master/CHANGELOG.md

That said, you could try swapping out the react version in your project, but if you hit weird bugs (and I suspect you would) you'd probably be on your own. I'm sure holmsand would be thrilled to have people chip in on keeping up w/ react changes.