The Penumbra dialogue doesn't really prove anything - if Insurrection is set after the war, it makes sense the Federation would want to try to work with the Son'a. The war is over, they are no longer enemies, and they are working together in an uneasy alliance for mutual benefit.
On the other hand, if Insurrection is before Penumbra, why would Starfleet work with a current enemy? Riker says they produce (or produced?) Ketracel White. As far as we know, there can only be one customer for White. As Troi says, "why would we be involved with these people?"
Interestingly, Riker calls it a "narcotic" which opens up a possibility. Let's say they were a Dominion ally during the war. They got rich selling White to the Vorta - rich enough to fund their vast battleships, illegal weapons and atmosphere-stripping super ships. After the war, why would they still make it unless there's a new market? Perhaps it was found it has an addictive effect on other species and found a new life on the intergalactic drugs trade?
In terms of timeline, Insurrection is vague enough with all of these questions that you could argue either way where it's set. Personally I think it makes more sense just after the war, but YMMV.