In my research group, there's a story that one of their collaborators once tweaked the interline spacing to get under the page limit. Apparently the end result was that you could riffle through the printed proceeding and tell where his article was, just because the pages were darker.

So yeah, it probably happens. If it's half an hour before the submission deadline and there are four lines left on the page you have to cut, you'll do what you have to to get the job done. =)