Would the fixture canopy bring the pancake into compliance?
Probably not. Only if it is listed with its volume can it be used for the purpose of box fill. I don't have my book here, but I know there is an exception in art. 314 (exception 4???) that says that a non-listed domed fixture can be used to deduct up to four conductors and 1 EGC that originate
from the domed fixture, but even still I very, very seldom see a light that is listed with its capacity.