Well think about it...Tarrlok is 37 years old in the series, and born in 133 ASC (After Sozin's Comet) And Yakone had his bending taken away by Aang in 128 ASC, about 5 years after the blood bender lost his powers. So it had to be the genes that did it for Tarrlok, not Yakone being a blood bender while conceiving him. You can see for yourself here
[link] and
[link] and compare the dates from when Tarrlok was born and when Aang took Yakone's bending. Thus conjugal visits have to be allowed or he escaped for Tarrlok to exist.