Dual is like solo but more. All classes are viable solo. Ipso all class pairings are viable dual.

If you're not trying to make a complete party/raid, do what's fun. It helps if someone can heal, it helps if someone can take hits, and it helps if you don't have puny damage output (although these days I'm told even holy priests can kill mobs instead of just healing themselves perpetually until the mob gets bored). Hybrid classes or specs are fine, even encouraged.

So...yeah, it works.