I wouldn't do it simply because I've had bad experience with it, but I have heard a few successful stories.
Guppies tend to be very nippy and will often times tare the betta's fins. I tried putting my male crowntail in my community with a bunch of guppies and while he didn't bother them at all, the next morning I found him hiding from the guppies with his fins all torn. I have a picture of what he looked like after the guppies had there way with him, but unfortunately it's not on this computer.