Consider protected oral sex to reduce any risk with future partners; better yet, know your own herpes status too (and your partner's!).
A one time encounter is low risk, yes. As a whole though, Oral sex IS in fact a risk for herpes transmission. About 1/3 of all new HSV1 genital herpes cases are from oral sex. And more than 1/2 of all new cases amongst the college-aged crowd. I can vouch for it's transmission, as I have genital HSV1 from my partner who has oral HSV1.
We don't have any real stats on Valtrex preventing the spread with HSV-1 oral with shedding. Atleast nothing I have seen. Your partner was incorrect in stating you can't get HSV-1 from a blow job. You can get genital HSV-1 from a blow job by a person who is either actively shedding the virus or actively present with lesisions.
Oral sex is considered a LOW risk for herpes transmission. This doesn't mean no risk it just means it is small.
My advice unless you see any symptoms consider yourself in the clear. You will display symptoms typically in the 2-20 day range. My other advice would be if you do not have a Herpes test done I would advise getting one to know your own status. You need to get a type specific IgG test. If you decide to test later on for possible infection from this encounter wait 3-4 months (12-16 weeks) to ensure your status. Hope this helps!