Genital herpes may be caused by either HSV 1 or HSV 2. Meaning if you get cold sores on your mouth and you go down on a chick, she will get genital herpes and it will be HSV-1. It works the other way too, if she blows you and she has cold sores on her mouth (which many if not most people do) you can get sores down there.
From some STD research I've done (as I have cold sore outbreaks on my mouth and I was worried about spreading it) it seems that if you get HSV-1 cold sores on your mouth you may be much more resistant, if not immune, to HSV-2 which causes genital herpes, and pretty much 100% immunte to genital herpes caused by HSV-1 (which represents only a small percentage of genital herpes in the USA but nearly half if not more than half of genital herpes in the UK).
This is because you can only get infected with a certain strain once, and it is very rare for a strain you already have to infect another part of the body (very rare, though not unheard of).
I don't know if a person who reguarly gets cold sores is more or less prone to getting genital/oral herpes as opposed to a guy who gets no kind of cold sores or visa versa.
It seems like you would be far less prone.
Still, its not a good idea to do anyone dirty. And I am not a doctor so feel free to verify this information elsewhere.