They're basically attached as if they are <script> tags, but in worker mode it uses importScripts() instead. It shouldn't matter either way, basically they just run in the same context as the runtime.
Minification is an interesting question and not something I've fully figured out yet, but I suppose yes, if you enable minify it will minify all your own JavaScript too. That means you need to take in to account how to write minify-proof JavaScript.