Yeah, I think Omega around 12 at the start of
The Bad Batch, so she would be around 40 by the time of Ahsoka's show. Unless Omega ages more slowly than normal, she can't be the young woman with the orange lightsaber. I also can't really see Omega becoming a bad guy.
EDIT: Yes, that is Ivanna Sakhno playing
Shin Hati, the apprentice of Ray Stevenson's
Baylan Skoll. (Interestingly, Stevenson previously voiced Gar Saxon.) They are clearly antagonists, but their exact relationship with the Jedi and with Thrawn remains to be seen.