Regarding the reason for SRM recommending grease, my mate Geoff fitted one of their conversions years ago, dry, as there was no mention of grease by SRM or anyone else. His belt broke recently, it had cracked up around the edges and the teeth had been worn away somewhat as well. He bought a new belt from SRM and was told to apply grease.
So, it sounds like grease is necessary but purely to give the teeth surfaces a bit of lube, so I wouldnt fill the space as you do with the chain.