Might be more trouble than it's worth, but is it?
These guys seemed to have figured out how to attend college without paying tuition.
Sure. You can get away with attending "larger" college classes without being enrolled, but that would only be worth your time if you didn't care about getting credit or a degree in the end. You wouldn't be able to take any exams or tests either because your name wouldn't be in the system for grading. But if you insist on getting that FREE education, some instructors don't take roll and usually don't remember individual students in their classes.
As an alternative to simply crashing classes, there are plenty of colleges that welcome non-degree students. There are many people that sign up to simply take a class or two. There are even free online courses available online!
So is it worth your time to crash a class or two to learn for free? That depends if you need that degree or not for your resume.