I was recently at a wedding in Lawrence where I met Berel Feinstein, R' Moshe's grandson. He told me he was there when Saba came to meet R' Moshe in 1984. He told me that he met Saba and saw the Petek, and was also present for Saba's meeting with R' Moshe. I asked him what his reaction was to meeting Saba and seeing the Petek. He told me he didn't really know what to make of the Petek but that he felt immediately that Saba was a very special person. He told me that Saba came with two guys, one of whom was the grandson of the Baba Sali. He told me that R' Moshe was shown the Petek and then Saba told him the story behind the Petek. When I asked him what R' Moshe's reaction was to it he said that R' Moshe didn't really say much but rather just mostly listened to Saba. He also confirmed that R' Moshe wrote the haskama. I asked him if R' Moshe accepted the Petek, his reply was "well, he didn't not accept it." So I said, "considering in the haskama he described the petek as "a very wondrous thing" (among other things), it seems preety clear that R' Moshe accepted it." To this he agreed with me.
My wife, who was also there, then interupted the discussion and asked him why he's not Na Nach now and doesn't wear a Na Nach beanie. He just kind of shrugged. she exclaimed to him "we want to make you Na Nach!" To that also she did not get much of a reply.
The last thing I asked him was what he thought R' Moshe would think of the people following Saba today (a.k.a the Na Nachs). He told me that R' Moshe always approved of anyone who is following their Rebbe sincerely.