I don't think this can hurt, but it probably won't do any good whatsoever.
The reason is because there are SO many alumni that could potentially recommend someone. Just imagine if each year, the top 10 students of each graduating class for the last 5 years recommended one student - that would be 50 students right there.
Truth is, unless it's a current Harvard Law professor, a supreme court justice or someone who has a building named after them at Harvard, an alumni rec isn't going to do jack.
I'm lucky enough to work for a UCLA Law grad who is not only on the UCLA law school board of trustees, but is also a superior court justice. I had him put in a call for me. I'll let you know what happens.