Most of the conflicts you're seeing are probably more cabal-based than class-based, or they're based on the individual RP of the character in question.

For example, the Outlander cabal dogma rejects conjurers. The druid you ran into might have been a member of this cabal, or might be an aspiring member of that cabal. It's not uncommon for veteran players to create characters with beliefs largely in line with or at least not conflicting with in any major way the cabal they hope to join.

Alternately, this could've been part of this particular druid's role. Empowered characters such as shamans, druids, healers, and paladins frequently have relatively well-defined belief systems. That doesn't mean that every or even most healers will have the same enemies list, but it's likely that a healer character will have a pretty good idea of who his enemies and allies will be, though this need not be class based.

Paladins and many other good-aligned characters will, as you say, shun and often hunt obviously evil characters. Beyond that, it really does tend to come down to individual RP, which itself is often shaped by existing cabals and religions.

Oh. Finally, not every cabal will have titles that give away their cabal membership. On-duty Tribunal do and members of the Empire cabal do; prominent members of some other cabals, especially cabal leaders, often do as well, but this is not a hard and fast rule.