It most certainly does shutdown the HPTA. I've seen it proven several times on people's bloodwork having test levels lower than their 80yo dead grandmother post halo cycle. Any hormone will shutdown the hpta, even 1,4-Andro.
I'd recommend using the E-Control in the last 3wks of your 6wk PCT to help prevent aromatization of the testosterone created by the nolva, and in turn prevent any chance of estrogen rebound and in turn the possibility of gynecomastia.
As for Nolva, it is a toxic substance just as much if not more so than many prohormones. More than 20mg is not necessary. I'd recommend just 20mg every night prior to bed for the first 4wks of PCT.