
In omegaverse everyone can get pregnant and everyone can impregnate so yes a beta can impregnate an omega. Even omega can impregnate another omega. When an alpha bits an omega they become a mate and omega can't have sex with any other alpha than their partner but in this story the omega forces himself to have sex with the beta because he loved him. In their first time doing it (after being bitten) the omega threw up but later his body got used to it and now can have sex with the beta freely.
Betas have more resistant to an omegas' heat than Alphas that's why he didn't felt the omega's heat but sometimes if the heat is too powerful it can effect the beta.
These kinds of things always depends on the author since the omegaverse world don't really have any rules~
I hope this helps (=・ω・=)

In a lot of the omegaverse stories I've read, it's also mentioned that an omega who doesn't accept the alpha's bite, the mark disappears after a time, so it's possible that, rather than just getting used to sex with someone else, the alpha's bite mark just disappeared.
Okay, I'm really confused...
A Beta can impregnate an Omega?
And if that (asshole) Alpha bit him, he shouldn't feel good when having sex if it's not with his 'partner', why he still has the mark and feels and good when having sex with the Beta? (oдolll) I'm so confused–
And why it was almost like the Beta didn't feel the heat of his Omega?
Anyway, I really loved this manga, even though I almost dropped it when that fucker raped him and bit him… He didn't care at all about his Omegas, all he wanted were kids… Omg I hope he rots in hell. ( ̄へ ̄)