HIV can spread to a partner by oral sex. HIV can spread by vaginal fluid, semen or blood. This information is according to the Center of Disease Control and studies have been done on this topic. Semen and vaginal fluids could enter a partner's body by oral sex. Having safe oral sex greatly reduces the chance of catching or passing HIV to a partner.
Herpes can spread to a partner by oral sex. HSV-2 is genital herpes 90-95% of the time and oral herpes 5-10% of the time. The chances of genital HSV-2 spreading to a partner orally by oral sex is low. Genital HSV-1 isn't common. HSV-1 is genital herpes about 5-10% of the time and oral herpes 90-95%. The chance of a partner catching oral HSV-1 from performing oral sex on a partner with genital HSV-1 (which is common genitally) is high.
So safe sex with herpes is necessary.