The problem here, as Kharhaz stated, is that the rules for using a Vine as the source prevents you from targeting anything outside of the vine's zone (or a wall bordering it). It doesn't matter what the range on the spell is, when you use a vine as the source you are limited to within that vine's zone (or a wall bordering it).
Now, if it's just the Necromancer who has obscured and not the whole zone, you could target a vine in the zone with the Necromancer to attack them.