Dreamwidth membership is not required. You can read the posts and comment using the non-user options like you just did.

The Bingo Card Generator is not on DW so you can make your own cards there.

You may post fills wherever you wish. AO3 is fine. Some people use LiveJournal, a personal website, or other venues. Then just claim your bingo by posting here as a non-user.

allbingo doesn't require people to post fills though. You can just list what you've written without a link if not all of it has been released online. Some folks are writing original work and/or selling it instead of doing fanfic like most bingo fests use. So we allow claims without posting because otherwise it takes forever. I've had cards almost full without being able to call bingo because they weren't all posted.

I hope this helps.