Geographic tongue has no real secondary issues. However, when talking about oral sex, your mouth is one big open wound. The tissues in the mouth have the best absorption in the body. Blood and other fluids get into the body extremely quickly through the mouth, nothing will protect you from that.
I've been trying to find other people with geographic tongue, lately no luck. If you are still reading this thread, does your geographic tongue brush off when you use a toothbrush or tongue brush on it? I got the fungal swab by a doc who said mine isn't thrush/candida, and that it looks like geographic tongue. I just want to confirm with someone else that theirs brushes off too.
Also, that comment up there about the mouth being a big open wound... nuh uh, keep in mind that the mouth and the nose are the first line of defense for the body. Mucus neutralizes a lot of things. As well, your mouth is the start of your digestive system, it gets to work fast and dissolves things that enter it very quick.