And to ask more generally - what about Pact member relations with other AQ powers (Cardassia, Ferenginar etc.) ?
I'm not sure we have much information. Most of the Pact members were previously isolationist if not full-on xenophobic, so there's not too much of a history with other nations, as far as I can tell.
We know some things about Pact nations' relations with the Cardassians: Cardassia had minor conflicts with the Breen and Tzenkethi (the "Terok Nor" books established- or at least suggested- that there were border raids and jostling and sabre-rattling there, but not actual war, apparently). "The Lost Era" revealed the Cardassians bought weapons from the Breen, using the Orion Syndicate as middlemen, while DS9 established they have an embassy on Breen homeworld (or the planet the Breen SAY is their homeworld, depending on what we make of Weyoun's comments, I suppose
). "A Stitch in Time" mentioned an abortive attempt by some Romulan factions to create an alliance with Cardassia and put an end to their isolationist phase, but the majority in the government seemed not to support it, Tain's manipulations aside, and nothing materialized...The book also said the Tal Shiar and Obsidian Order were essentially in a state of war. There's a Cardassian embassy on Romulus as well (I don't know if they have one on Tzenketh or Ab-Tzenketh, I don't recall anything about official diplomatic relations). As for Tholians, Gorn and Kinshaya, I don't believe there's been anything of note (Gorn are too far away, I guess, Kinshaya didn't talk to anyone and Tholians didn't either, although a Tholian ambassador visits DS9 (ambassador to Bajor?) so they might have a diplomatic presence.
As for Ferengi, they'll trade with anyone, more or less, so if any of the Pact nations desired it, I'm sure there'd be relations there. The novels suggest the Ferengi bought warp drive from the Breen, or a Breen (I don't remember if it was their government or independent traders) while DS9 established they trade with them.