Faction exclusivity doesn't matter on a server with cross-faction grouping.
So Horde having paladins and Alliance having shamans should not be a bad design.
Epoch obviously has these 2 race/class combos and I have to say the Undead Paladins just look so good.
I understand some lore purists might object, but honestly it's not a big deal. Humans were paladins and then turned to Forsaken. Undead Priests wield the light too and did ever since 2004.
I am more opposed to Dwarf Shamans. It just screams "Cataclysm" to me.
and on a cross-faction grouping server, you don't need to give both factions both classes. I would be happy with Horde getting Paladins and Alliance getting nothing in return. No need to cram Shaman onto a Dwarf, where it doesn't fit as nicely as a Paladin on an Undead, just to keep it "balanced"