Honestly I couldn't tell you from experience though because I have a 6700 and Sprints page says the Mogul runs WM6. Anyone have one?
There are a couple of threads here too about WM6 for 6700...
http://ppcgeeks.com/what-is-the-big-...che-t6486.html
http://ppcgeeks.com/when-can-we-see-...700-t5028.html
But I don't think they mention the mogul specificly, just that the nk.exe needs to be written for the device.
Edit: Ok.. four or 5 posts down in the first link they mention Mogul has WM6 allready.