My WvW Necro Build
I honestly run Reaper just for the shouts as a midline fighter. When the zerg pushes into your group, getting chilled to the bone off with two wells and a tone of staff marks onto the ground can generally rob/strip a huge amount of DPS and burst from their push.
I think Reaper can be good as a mid line, but over all damage seems to favor the classic back line wellomancer. I just couldn’t get in to Reaper for group play, I think it would be pretty good for roaming at least.
Added my necro roaming builds: http://asphyxia.tv/wvw-roaming-necromancer-build/