Kohanim do not look for a heter–they just don’t go. that’s all.
I know the wife of a Kohen who would not go “walking” (favorite sport of women) through a non-Jewish cemetery just “in case” she was pregnant with a boy.
I have a brother-in-law who is very careful about “body parts” in museums and won’t go and won’t let his sons.
Even non-frum Kohanim are careful about the halochos of not going to funeral homes and cemeteries.
If they are makpid, that is their z’chus. Hashem gave them a role and, with it, obligations. They take it seriously. Good for them.