Why does it matter that they can't run? Just warn a player before he chooses to play as ghoul: you can't run, you can't use specific weapons, blah, blah. People can make choices themselves and take the consequences.
No, you're silly - have it implemented and next thing devs can expect is "zomg give some better stats and things, becuz we can't do this, this and this""Zomg nerf encounters, we cannot run""zomg nerf thieves, we cannot run"...
If you want to make enemies, try to change something.