To talk about "safe" vs. "unsafe" is an oversimplification. Risk has to be measured along a continuous scale. For example:
Jumping out of a second-floor window might be less risky than jumping out of a tenth-floor window. Does that mean jumping out of the second-floor window is "safe?"
Driving 100 km/hr on an icy road might be less risky than driving 200 km/hr on that road. Does that mean driving 100 km/hr on ice is "safe?"
There is risk of disease transmission in unprotected oral sex–even without ejaculation. It's less than the risk of disease transmission from unprotected anal sex with ejaculation. That doesn't make unprotected oral sex "safe."