Will a RouterBoard 133 work as a wireless AP?

Thank you

Yes.

I just built a couple of AP's for subscribers using RB133's (not RB133C)... Still too expensive to compete with off the shelf cheap-o wireless routers, but OK when some special needs exist.

RB133's come with Level 4 license.

Early versions of the RB133C came with Level 4, though I believe that they are now, or will soon be coming with Level 3 license.