it was indeed an invitation to discuss an expanded alliance. Donatra and Rom had agreed to attend.
I'd expect the IRS to join. Donatra'd join largely to piss off Tal'aura and also to make sure she had allies if the TyPac invaded.
The Ferengi might not. Rom might decide it made more sense to sit it out and be neutral, Nan could even persuade him to stay neutral to act as a go-between.
i'd be more inclined to see the Cardies and the Talarians joining, if only to guarentee aid in rebuilding their devastated fleets.