You get diseases, undead pets and even stuff like clawing to atk from afar. If you go with Rider, mobility is even better. Unholy actually got one of the most flexible toolkits in terms of range.
In general, evokers are clunky. You either get a lot of with Hover or end up like mid-range turret.
I’d go with Unholy DK. Evoker dps feels too restricted.