No one has ever played a gnoll in any game I've been in. Gnolls as a species in my home campaign have always come from a dark place. Most are monstrous raiders, but there are a few exceptions, and I am open to someone playing them as a PC. Even if they are monstrosities. That said, I don't have a problem with gnolls being monstrosities. I have had good aberrant mind flayers, monstrous medusae, even fiends and other monsters as exceptions, and that would be no different for me.
However as a DM, I introduced a lone gnoll female NPC who had joined a cursed pirate crew. Her curse was being good so that she was incompatible with her people's ways and would always be a lone outsider. I was a little twisted when developing her backstory, in that she wanted nothing more than to be a mother, but couldn't stand the evil ways of her people. She became the pirates' "party mom" who whooped enemies if they harmed her adopted "family." I really liked her. She eventually became captain, and an ally of the PCs. Her story arc led to her best friend and first mate being killed, who was then reincarnated by the PCs (randomly as a gnoll!). They fell in love and had a family.
I also introduced one redeemed tribe of humanoid gnolls as NPCs in a separate story. No storyline traction with them though. PC's moved on.
