A lot of this goes on, to the point you should consider the possibility that a negative reference for a senior job from someone you don't know may actually have a negative correlation on the value of that potential employee.
The fact is a lot of bosses are jerks, and they know it, so when someone leaves who they've either mistreated or tried to compromise in some way, said boss experiences night terrors and what might be alluded to once the escapee's outside the ringfence.
Bottom line - accept employee references only from people you know.
You want the best employee and you can't afford to lose them to some unknown idiot's professional insecurity or spite. 
That said, you also want a warning if someone is a jerk. But only if they actually are.