Probably not worth fighting. Your first HOV violation has no points, and a $125 fine.
The Code of Virginia for HOV talks about "highways" though, and although I don't see a specific definition of "highways" in the Code, it seems unlikely to me that the on/off ramp lanes have been explicitly designated as HOV lanes. The CTB has designated "the inside (the beltway) lanes on Eastbound I-66 during the AM peak hours (5:30 a.m-9:30 a.m.)" are restricted, and I guess that leaves up to discretion of whether or not the ramps are included with this. But I doubt the cost of fighting it would be worth it at all.
http://leg1.state.va.us/cgi-bin/legp504.exe?000+cod+33.1-46.2