Yes. I forgot which chapters but it mentions "besides dojin "mom" everyone are alpha".
So it's possible if his mom is a male omega. Like every omegaverse fics, the one who give birth will be called mom and sometimes dad.
She isn't obligated to marry or to find a mate, though fargo once shared a drawing of her fricking a male with her peepee, cowgirl style
https://13-fargo.postype.com/post/6198409 (also need to login for age confirmation)
is dojin's parent both male? and does his sister also need to marry female or is it male?