Hi
If he (yourboyfriend) has tested for the uclerative STDs, (herpes, syphilis, and gential warts) at 3 months after his last possible exposure and has negative testing then yes, he has another skin condition not related to STDs.
Re-read what SadHeartedLeo said about STD testing making sure you include herpes.
idk, but i had the same problem, me and my boyfriend both had sores ans redness, he even had dry skin on the underside of his penis. I'm pregnant and i've been really vaginally dry, so we're thinking it was just too much dry sex (we had like a marathon type thing right before the redness/sores showed up) he went to his doctor and his doctor said it doesnt look like herpes (we were afraid of that because its the only thing not included in the tests we both had done) and when i went to the clinic, the doctor was like "omg, you have herpes... idk how you could let yourself get this bad" which, made me almost cry while the womans got me on a table in stirrups. she gave me a prescription to treat herpes before the test results even came back, i havent heard anything about it... my condition had none of the characteristics of herpes other than redness and sores... which could honestly be a number of things.
the moral of my story is, you should get a second opinion... make sure herpes was included in the bloodwork, and make sure if its not and he still has sore to have it swabbed and tested, and actually get the results back. because i'm having no problems, the sores and redness were only there for a few days, and the doctor i saw and my boyfriends doctor have 2 completely different opinions on what it is. so, just check for everything before some doctor makes a decision that changes his life forever.
i hope this helps... sorry i went on a bit of a ramble.