The Collective hasn't allied with the Romans so much as attached themselves like a parasite to their war in order to take advantage of it and steal Abh worlds to experiment on the population and decide whether augmented Abh would be useful to the collective or whether they should simply be recycled into new synths.
Such fun, I do believe this is going to end rather badly for the poor old Abh
The Abh are supposedly thrice stronger than Romans who are already stronger than normal humans, with their ability to interface with their own computers. I'd say they'd be useful.
Also, I smell a galactic council comin round. ... I can also smell a "No Abh invited" sign.