Heh, there are a whole bunch of people I've seen multiple times with different acts who don't appear in the list otherwise.
Ripper Owens, for instance. Twice with Judas Priest, twice with Dio Disciples, and once solo.
Or Doug Aldrich, three times with Dio and twice with Whitesnake.
23/4 Scott Stapp
25/4 Spirit Caravan
30/4 Kenny Wayne Shepherd