In a hypothetical sense, it is true. It a realistic sense, it would be unlikely that you would acquire herpes via condom protected sex. Not impossible, but very uncommon.
Wherever you are getting your information is probably either misinformed or taking a very conservative view. It like saying that I can not guarantee you will not die in a car accident tomorrow, but it is statistically unlikely you will.
Oral sex is safe sex. Not completely risk free, but much lower risk than unprotected vaginal or anal sex. Because oral sex is an inefficient way to transmit STDs, the vast majority of oral sex events do not lead to an STD, but your main risks (and these are low risks) are herpes from hsv1, gonorrhea, syphilis and nongonococcal urethritis (NGU).
There is virtually zero risk for protected oral. Likewise, performing oral sex on someone is very unlikely to result in a partner's genital infection being transmitted to you and resulting in an oral infection.
Your asking about STDs. Mouth to mouth deep French kissing does not lead to an STD.