Yes, Yes, Yes, Homeschoolers go to collage! Cafi Cohen even wrote a book about it called "And What About Collage". In it she talks about creating a "home-brew" transcript. It's really good information, although if your children are young, be aware that htis is an area that is likely to undergo major changes as the number of homeschoolers in the country increase.
What I have also seen recommended in a lot of places is to contact the individual schools that you are interested in during your child's early high-school years to get a better idea of what to learn and how to present yourself.
Home Education Magazine occasionally has stories about what older students are doing, and they even had a column for a while called "unscholler in collage" (that is until he left collage to continue his unschooling career - he still writes the column under a different title - very interesting reading.)
So far as unschooling in states with stricter regulation - the answer is yes, it can be done, and you can bet there are unschoolers all around you doing it!
It is important to make contact with local organizations to find the information you are looking for - the climate is different in every state, and sometimes even from district to district! Call every contact you can find even if the organization does not seem like it would suit your needs - you never know who will point you in the right direction. Especially in the unschooling community, sometimes the groups are smaller and not as visible, but they do exist.
You do need to read your state's laws yourself - it can be dangerous to rely on other's interpretation of the law in any area. But, with that said, as you talk to more people you will probably find that most people sort of comply in the same way - KWIM? For instance, for an unschooler, it may be possible to have a portfolio evaluation in lieu of testing.
ooh - this is long, I'll leave you alone now. But do search for support groups everywhere - on like, health food markets, bookstores, libraries. . .you'll find lots!