I believe you can report this tax perp on an anonymous basis. However you must be squeaky clean yourself. I don't think I would do it. Could be traced back to you.
However if they were out and out bad ie. thieves, vandals,drunks, druggies, dogs barking at all hours then I might. Complete scumbags yes. If not no. It is quite possible they will get audited anyway because how long can they get away with it?
If it was me no......