The talent "All Will Serve" does not function in PvP instances. The Skulker will simply follow the Death Knight around in BG's and Arena not doing anything at all. Laziest undead I ever did summon. Hopefully Blizzard will fix soon.
Well he certainly doesn't mind getting his exercise in, as he'll gleefully run beneath you while you're using an antigrav pack in mechagon, aggroing any and everything on the ground beneath you.
“Do not lose time on daily trivialities. Do not dwell on petty detail. For all of these things melt away and drift apart within the obscure traffic of time. Live well and live broadly. You are alive and living now. Now is the envy of all of the dead.” ~ Emily3, World of Tomorrow