I can only supply a very small glimmer you might want to follow up.In 1770 or so a John Pendergrass in Bute Co NC apparently married Margaret Pownall, daughter of John and Margaret Pownall.Their first known child was Nathaniel Pendergrass born c. 1771, and there is a known John Jr and another boy whose name escapes me right this minute.There was another John P in the same neighborhood (with a William and a Spencer P) but the exact relationship of the two Johns is not known. DNA testing shows a relationship but the ages are a bit wonky for father/son (but we just don't know.)
Now, what MIGHT be of interest to you is that John Pendergrass, wife Margaret and her father John Pownall were gone from Bute Co (now warren and franklin counties)sometime before or during the rev war (after 1771 when John P and John Pownall are on a tax list in Bute) and show up on a deed in Lancaster Co SOUTH Carolina in 1779. One of the deeds references John Pownall and North Carolina and even, I think, Bute Co.
There are two ways to see if you might tie in with Nathaniel P's descendants.One is to buy the book by Robert Pendergrast of Atlanta, Georgia (he's listed in the phone book) and check the index (the book is very well indexed) OR you can check the website hosted by Dave Pendergrass (you'll have to google or heck through this forum) which incorporates a lot of the info from Bob's book, as Dave descends from one of those brothers.
It's a long shot,as you say, but Pendergrass is not a midle name that someone would give a child without a really compelling reason ! Also, there are lots of Nathaniels in that branch of the family (not in mine)
I am at work now, but I do have a copy of Bob's book and will check the index for you when i get home.