Again, not sure they can actually do that based solely upon accusations that cannot be confirmed. Of course I do not know how that process actually works, but I would think he has some course of action. If nothing else he can argue that the ethics are in no way being consistent in their handling of these types of cases.
No reason why they can't. The Ethics Committee is supposed, "...to receive and investigate allegations of improper conduct which may reflect upon the Senate, violations of law, violations of the Senate Code of Official Conduct and violations of rules and regulations of the Senate; recommend disciplinary action; recommend additional Senate rules or regulations to insure proper standards of conduct; and report violations of law to the proper federal and state authorities." It doesn't have to be criminal to "reflect upon the Senate". And the rules of evidence don't have to be followed. They can use testimony unsupported by physical evidence, hearsay, whatever.
If nothing else he can argue that the ethics are in no way being consistent in their handling of these types of cases.
In an environment where nobody wants him there to begin with, attacking the committee for inconsistency is not going to get him far.