Yes, nier requires the subjunctive:
Il nie que ce soit vrai.
He denies that it's true.
Il ne nie pas que ce ne soit vrai.
He doesn't deny that it's true.
Why ce ne soit vrai? It's the ne explétif
The Subjunctivator! | Quiz: Subjunctive or indicative?
Does nier need the subjunctive?
Verbs, expressions, and conjunctions that require the French subjunctive
By Laura K. Lawless, About.com Guide
French Subjunctive
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- Nier - French Subjunctive