If I accept a petitioner whose spouse is imprisoned as a result of a failed raid (by someone else), would I get an option to make a raid to release said spouse and have the spouse join my fortress (or at least a chance to bring that prisoner back from a "normal" raid, with the same join fortress option)?
My fortress is quite a fair bit away from being in a shape where raids can be attempted largely due to an onslaught of infiltrators and goblin invasions (with the impact in that order), so any investigation on my part would be a fair bit into the future.
Raiders seem to rescue random imprisoned people on general raids, so you could try that. That's how Toady explained it as working (which is what the Petition for Sanctuary mechanic is supposed to be for).
I've seen that, but the extension of whether you can use it to reunite couples is what I'm unsure about. I guess I'll eventually accept a petitioning goblin with an imprisoned spouse, but it will probably be a fair while before I'm ready to try that.
Edit: And another outlier question: What happens when a squad member is due to give birth during a raid (My #1 fighter is also one of my two human mothers)? I'm still a fair bit from actually conducting raids, though, so she's probably fulfilled her procreational duties by the time a raid is in the cards (assuming Chronos isn't faster...).