I think the best evidence that they are friends is that he’s comfortable enough to go to his bucket in front of Quark when they first bring the Defiant to the Gamma Quadrant in The Search. Even though he’s grouchy and says he doesn’t want Quark to watch, the only other people he’s allowed to see him revert to his resting state were Lwaxana and Nerys.

It’s always good to have someone around you who knows exactly where you stand.

also the part in the finale when quark basically begs for recognition and nearly cries.

Like a good pruno, it’s toxic but strong!

Frenemies