A friend just had this happen at his consulting company:

"Discrediting an employee's current company - Black hat recruiters will contact an employed potential candidate and tell them that their current company is in a precarious financial state and offer to find the employee another job. Black hat recruiters will even do this to employees of their own clients."

He let one of his employees go and they went to a recruiter to find a new job. Next thing you know, everyone at the company was getting called by him saying they were in financial trouble and that he could find them work.

A few days later he calls my friend up and says "I know you've been losing a few employees, I think I have some good candidates if you're hiring."

From my dealings with recruiters, this is almost standard practice.