Dead Man Walking will be circumvented by anyone with Mind Blank, or with a class immune vs fear, like Paladin. Which is a bit silly, as someone on the Discord pointed out, there would be in-character cause to ask someone to dispell your mindblank, and lure over a creature with a fear aura, so you can boost your open lock skill a couple of points to open a locked door in a dungeon, instead of simply treating it as an auto-success if immune, which is how it should be treat imo. In that way, this 'general' feat with no requirements could be a applicable to Paladins as well, which as it stands, would receive no benefit from it.
..So my suggestion? Either restrict this feat from feat selection for Paladins, as it can be potentially misleading and a dead/useless feat if taken, for Paladin players. Most would, in common sense, assuming being immune to fear dictates an auto-success, instead of rules-lawyering the fact that since you were immune, and thus disallowed to make a saving throw, that you then do not count as having 'passed' the saving throw.