Well he's an alpha..and he got pregnant. In the end it's all made up and there's nothing stopping the BL artists from going "know what? I want the alphas in my story to get pregnant." In the first place males do not get pregnant anyway so..
Yes Alpha x Alpha the uke can be pregnant
They all can get pregnant. but alphas (esp males) have the lowest chance of getting pregnant. While omegas (esp. females) have the highest chance of becoming pregnant. betas are in the middle
In omegaverse alphas can NOT get pregnant, and it's not just a matter of taking it in the butt, it's supposed to be a biologic thing. That's why omega are so interesting, because they can. Story was ok in a general mpreg way, but not omegaverse.