No, if you have entries you can't judge that style category. There are 23 categories though so its usually not a problem unless you enter a whole lot of beers. The only problem is if you enter categories you really enjoy, then you can't be assigned to judge those. They will usually ask you what you want to judge, and sometimes you get one of those.
I entered in light lagers, amber lagers, and sours. I judged German wheats, Belgian and French ales, and Specialty beers. I liked the weizens, I have experience brewing those. I also have experience with the Belgians but I'm not that big of a fan of the phenolic character anymore. The Specialty category was all over the place. I think the worst are the dark beers, 10 stouts and your palate is toast.