I was drawn to Unity over other engine choices primarily because of the Flash compatibility. Flash is the main platform I want to develop for. And Unity seemed superior to other choices for flash. I am not sure if I want to commit to buying the pro version before I see what the flash platform exports looks like on something I wrote. I understand I need to buy the flash add on, to publish in flash. My question is if I just buy the Flash Add on and use the 30 day trial, Can I publish something?

Unity make trial versions available to allow you to evaluate the product. If you want to publish a game, then Unity will conclude that your evaluation was successful, so will expect you to make a purchase. In your case I imagine you will want to use the free editor with the $400 Flash add-on. In fact, when you purchase the $400 Flash add-on and activate using the serial number that is generated your trial will end and you’ll have the free+Flash combination.