I don't believe such a "verified" list exists. Slim's "slim" nature means you can integrate just about anything with it, but also means you need to do just a bit of the configuration yourself. The list of packages and middleware that can be used with Slim 3 would be incredibly long and nearly impossible for an OS project to maintain.
1) Specifically for middleware, since Slim is based on PSR-7, you should be able to implement any middleware that follows the PSR-7 signature. For example you should expect most everything in PSR7-middlewares to work.
2) You should not expect anything that works in Slim 2 to work with Slim 3 without changes, as Slim follows semver you should expect things to break. Specifically, writing middleware for Slim 2 is much different than Slim 3, so middleware designed for Slim 2 would need to be updated to work with Slim 3.