I took a look this. Bitcoin doesn't reply fit any of these perfectly, but I think it is a URI in that it uniquely identifies a Bitcoin account. The issue is that Bitcoin doesn't really have a location function. I suppose you could say that you can locate Bitcoin address history, but that's not really the purpose of a bitcoin: link. I'm going to say no, it is not a URL. It is however a URN.
EDIT: mailto: is a URL the same way a HTTP URL is. It has a domain name and states the location for sending something. Given this example, I'll change my answer to yes.