Nah; Jim has made it clear that any of us can easily look up what he is in one of his Q&A sessions, and he was called a Watcher several times in Cold Days. From a Christo-Judaism standpoint, a Watcher is a class of angel. I don't have my references with me, but the Nephilim were scions of fallen angels, one of whom was supposed to have bestowed the gift of alcohol on mankind, according to the apocryphal books.
This info, plus knowing the way that Jim says he characterizes in books, make me believe that Mac is one of the Nephilim. Remember, Jim characterizes by using repeated phrases to give an idea of the character - so Karrin is always "somebody's favorite aunt with a button nose" and has terms referencing cuteness, Marcone is described having eyes the color of old dollar bills, etc. Well, Mac is always described using references to divinity - that he is, for example, proof that there is a God, and wants us all happy. This, plus "watcher", plus his respect to Mouse, makes me think that he came from an angelic source.
