It definitely does not fit the 'feel' of your classic paladin.
That said, paladins who follow a god who allows Rogue levels aren't likely to be your classic paladin.
I would say it depends on how you are portraying the engine effect. The original incarnation of sneak attack, backstab, would be right out. But if it's just a clever feint sprung on your opponent unawares, that ought to be fine. Paladins on the server before have engaged in surprise attacks on evil foes, or engaged an enemy from the side who was already fighting another person. Sneak attack just makes you extra skilled at doing so.
Dirty fighting is far more questionable and I would consider it a no-no for most paladins.
That's just my opinion, though, not a team ruling.
