Zahn is an awesome writer and I love him like burning, but from what I've read so far his romances tend to all be the same. Two people might be antagonistic to each other but for whatever reason they can't fight, they get close to each other, they find that they work well together, maybe there are a couple hints like pulling the "He's not my boyfriend!" trick, and then they just end up in a relationship. Never a madly passionate one, either. As far as I can tell it's always... comfortable. Which I like, really, and I like how he doesn't have to pair the mains up, but it takes some study to see when they start.
Shippers say Luke/Mara started with the Thrawn trilogy when they met, Mara wanted to kill Luke and didn't, they had to work together, and eventually they became solid allies. You really sort of have to stretch to see the UST there, though. Ten years passed in-universe, and authors writing there didn't use Mara much, but in the Hand of Thrawn duology Zahn came back and there was the hinting. Fairly blatant at times. The relationship really became formal in that scene in the drowning cave, which I still love.
I'm a Luke/Mara shipper, but not an ardent one. I like things comfortable.