I'm guessing that genital-to-oral hsv1 transmission is equally low, since I think the reason for the low transmission is that genital hsv1 doesn't shed as often as hsv2. I'm not sure about that, but that's what I think.
However, most people already have HSV1 orally anyway, so you could easily have a partner get a Herpeselect test to check for HSV1 and 2 IGG antibodies. (FYI, IGM tests are worthless. Ignore them if administered...or opt out of it if possible.) If he tests positive for HSV1 then he can't get it again orally OR genitally. I got the following quote from this thread:
http://www.medhelp.org/forums/STD/messages/1551.html
"With few if any exceptions, everybody with HSV-1 is immune from catching it again; and certainly nobody can be reinfected with the same HSV-1 strain they already are carrying."