I have a bit of a problem with the "qualifications" that the web site states for some of these people.
Just because some Irish tenor singer sings at a Republican function of whatever type doesn't necessarily mean that the tenor is conservative or a Republican. It simply means that he's a musician and that he, most likely, got paid for his work.
It's a gig, people.
As a confirmed musical whore, I'd even play for Lord Zero -- as long as the price is right.
And Don King is not what I'd called a ringing endorsement of conservatism or the Republican party.

ETA: A couple of these guys are dead. Ron Silver croaked a year ago. Ditto for Charlton Heston, though his passing was a couple years or so ago.