Dogs don't ejaculate. Not like you are thinking like with humans.
Male dogs often have what I think is called smegma, where they get a bit of discharge from their prepuce (the skin covering over the "red rocket"). It's just the natural process of cleaning out the area....that's probably what you saw.
Thanks all I just thought nothing came out since his testicales were cut off.
Semen is actually comprised of fluids from several glands (i.e. prostate and cowper's gland in humans, not sure if dogs have a Cowper's gland), the testicles just provide the sperm. So yeah, they can still produce the other fluids and ejaculate, but there's not any sperm. The lack of testosterone typically reduces the sex drive, so I would imagine that would make ejaculation uncommon...though not impossible. TMI?