
The short answer: it's your fanfic.:D
Long anwers, it depends on the rules of the universe the author created.
And for this world an omega can't impregnate anyone, the only exception could be (if possible) if an extreme omega turns an omega into an alpha, but then it would be an alpha. ^^
In KML it was mentioned that Yeonwoo can't impregnate anyone after he turned into an omega.
Afair it was mentioned on KMIYC concerning Josh.
And in DMIYC SPOILER
.
.
.
.
.
.
.
Dane mentioned it when he saw the omega twins.
And beeing an omega was his answer when a female accused him of beeing the father of her unborn child...which wasn't the first time.
JOSHUA, FORGET ABOUT CHASE. IMPREGNATE ME INSTEAD (You're an omega but you're still a guy so