Unfortunately I don't know a great deal about the various shader development tools out there.
My understanding of rendermonkey is that it contains a lot of pre-programmed and configurable features to make development of shaders easy. Things like Glass, texture generation, fur etc. It also has the facility to enter your own code I believe.
Using the pre-programmed features would be classed by the rules as using an external library of some sort. Directly entering code into render monkey, I would say is coding.
Designing a shader with a GUI and exporting it into your code is no different to using another media package to create music / gfx but if you've used the ready made features of render-monkey then you haven't really coded it, but the point of demos are to look cool / sound cool / be technically great or hopefully all of that.
That's just my uneducated understanding of Rendermonkey - if I am wrong I will be corrected.

I dont think that there's anything in the rules to stop rendermonkey projects being submitted, indeed it may well have enough value to merit a challenge of it's own in the future and prove useful in getting people interested in shader coding.
Anyway Las, if you want to enter something, please do - I've enjoyed the things you release into the scene and if people like what you've done then they'll vote.