A couple of months back I argued on another board about Chief and his kid. I was told that they've never stated that male Cylons can't father children by humans -- only that female Cylons can't get pregnant.
We know female Cylons can get pregnant - Athena had Hera, and Caprica Six is pregnant.
The issue was that the Cylons couldn't conceive together. They thought that a human might be needed, and so the Eight "recruited" Helo.
I called that horrible retconning, but I was actually shot down by the "If They Haven't Said It, You Don't Know It" Crowd.
I think that's actually a pretty good rule of thumb, actually.
We also know that they couldn't get pregnant before Helo came along. They were identical in all other respects. They didn't know why. But apparently males could impregnate human females, but none apparently ever tried.
Oddly enough, Tigh managed to get Caprica pregnant, but not have kids with his first Cylon wife, who was an older Six. (At least, that's how she appears in Tigh's hallucinations.)
I also remember that the secret ingredient in Athena's case was Helo's love for her.... which I don't think applied to Chief, whose wife might've loved him, but I don't think it was a mutual thing.