With enough power, and correspondingly good seeing to allow it to be useful, HM Sge is non-stellar. My notes from August, 2010 on a night I rated at 9/10 seeing:
"Tiny p.n., stellar at most powers. Starts showing a hint of a disc at 769x. Definitely non-stellar at 1099x and 1539x.
Responds well to UHC filter."