This is an example of what happens when I have WAY too much time on my hands...
I joined a mailing list called MTG-L, basically a bunch of rules questions and answers. Asked them this question. Got five completely different answers. Watched them argue about it all day. Eventually, it was ruled down to a part of K.11.7 (who the hell took the time to look through all those rulings? I went through the first five on Creature Type and gave up!):
***You can choose any creature type that exists on any Magic card in existance. You cannot choose the name of a card in Magic (unless that name is also a creature type), or any word that is in the glossary of the comprehensive rules or is otherwise used to mean something special under the rules. [bethmo 99/11/30]***
Basically, they agreed it doesn't work.
HOWEVER! The beginning of this line makes me question it. It has been ruled that you CAN, in fact, name any noun as a creature type, not just 'any creature type that exists on any Magic card in existance.' So... There are two conflicting rulings in existance simultaneously. I could've sworn nature abhores a paradox, but hey, who said WotC was remotely close to natural?
"Still seeking a viable answer..."