Nightfall is showing as requiring witch queen dlc, but the nightfall should be "PsiOps Battleground: Cosmodrome" and its a f2p map. My friend also can't start nightfall or even standard vanguard ops playlist because it tells him it requires dlc. We both got forsaken 2 days ago and since then I think something bugged out.
All vanguard op strikes/battlegrounds are f2p through the Vanguard Ops playlist, but to play the Nightfall variant you need the parent DLC. So yes you need Witch Queen for a Season of the Risen battlegrounds.
[quote] My friend also can't start nightfall or even standard vanguard ops playlist[/quote]
The Vanguard Ops bit is a bug, I've seen a report on that one, and it has been escalated to Bungie.
But it is correct that you can't launch the Nightfall without Witch Queen.