All STIs are low risk if there is no interecourse, i.e. no penis in vagina, rectum or mouth. Cunnilingus (oral-vaginal) is very low risk for all STIs, and so is exposure to saliva. Female "ejaculation" ("squirted in his mouth") is urine, which also rarely transmits any infection. The main infection risk from these events is gastrointestinal infection, like viral gastroenteritis (e.g. norovirus), but no STI. He also is at risk for common cold, influenza, covid, and other respiratory infections, if the escort happens to have any of these. "Red papules in her groin area" also is unlikely to be any STI.

In addition, in general STIs are uncommon in "escorts" -- meaning expensive female sex workers by appointment. Typically such women are well aware of the risks, take precautions (in this case, no intercourse), care about their health, and get tested frequently. In addition, their clients tend to be low risk -- men like your friend.

Are the STI risks zero? Perhaps not. But in my 50 years in the STI business, I've never seen a patient (nor heard of one) who acquired any of the standard STIs -- gonorrhea, chlamydia, syphilis, HIV, herpes -- whose only exposures were of the kind you describe. From a risk standpoint, I would not advise testing and would judge it is safe to continue unprotected sex with his wife. On the other hand, risk alone isn't necessarily the only reason for testing:  reassurance alone is a valid reason. If your friend is going to continue to worry after you forward this information to him, then 4-5 days after the event he could have a throat swab for gonorrhea and chlamydia; and in a few weeks blood tests for HIV and syphilis. If somehow I were in his situation, I would not be tested and would continue sex with my wife -- but it's up to him.

I hope your friend finds this information useful. Let me know if anything isn't clear.

HHH, MD