Sorry, I can't answer that definitively since it is not practical to test them in every possible situation that might occur on a website. However I don't know of any obvious reason why they woud not work if they are compressed.
The javascript files that our extensions use are all fairly small, they are all designed to work using mootools which is the javascript library that ships with Joomla, so there are no big downloads of javascript libraries required, unlike many extensions around which require JQuery or some other library. So mostly the size of the stylesheet and javascript files would be about 20k or so for a typical extension, though this could be reduced for example by removing whitespace.