In Scala it's very normal to write libraries or frameworks in "pure" Scala (i.e. not using reflection, annotations, proxies or anything like that), and all of those should be fine to cross-build for Scala Native (assuming their upstream dependencies do first). The state of libraries for Scala.js should be a good indication - anything that's cross-compatible with that is likely to work just as well for Scala Native.
I think the dependencies (like Netty for a web framework) would have to be migrated first. Scala native has a subset of java core libraries (from e.g. io, nio, util) rewritten in Scala, which could be a blocker if there's anything missing.