It is perfectly safe if there are no infections. It is a possible way
to become infected with diseases like syphilis (but then any open sore
on the genitals may facilitate that).

For HIV, the risk is much lower overall but it depends on a variety of
issues. The viral load in the ejaculate. The condition of the
recipients mouth (sores, infections, presence of alcohol, bleeding
gums may all enhance risk).

In short--probably better to avoid ejaculation with a partner who has
or may be HIV+ if you are HIV-negative.

        George M. Carter