Hi Greg,
Here's something to consider. You can trim the whole mask, ears and all and blend it.Now depending on what size flies you are going to tie let's say sizes 4 - 6 you would probably want to trim the fur as close as possible to the hide.If you are going to tie smaller flies it wouldn't hurt to trim the fur so it isn't any longer than a half inch. 1/4 to 3/8 of a inch would be ideal. Having varying lenghts kind of mixes it up and gives you a nice dubbing, you can always trim or pull the few long stray fibers after you tie the fly. This makes a good general hare's ear dubbing.
The Old Timers used to like to take the fur from the various parts of the mask: ears, cheeks , pole , face and make seperate dubbing mixes for each area. This good if you if you are looking for a certain shade or texture for the fly being tied. Some patterns like the hare's lug and plover call for a specific area of the mask to be used as does the Honey Dun that Pete hidy liked to tie.
Hope this helps.
Jim