I can think of few things that stale faster than persistently having NPCs unable to get past a character's exoticness. It stales for the player of the exotic, and it stales for the players of the other characters. My point is, bad DMs can stale the "exotic" races just as easily as they've staled the standard ones.
Sure. Of course they can.
If bad DMs actually use the exotic races. Because you know they are bad and likely barely reach for the exotic races outside of a rare forced token when they remember the race exists.
But like you say. If a Bad DM remembers it could easily get stale fast. Same as a player who player grazes the surface of one. shiver