I haven't been to the Moravian Archives, but I do know that much of the pre-1850s material there is said to be in a German dialect not easily readable even if one has studied modern German, so that may be why they mention (or possibly limit access to) researchers.
The Forsyth County Public Library on 5th St. in Winston-Salem has a good collection of local history and genealogy material in the North Carolina Collection, and "local" for this county can include material from Rowan, Surry, or Stokes, since Forsyth wasn't formed until 1849. (See http://www.forsyth.cc/library/Central/nc_room.aspx
.) The similar Stokes County research collection is in Danbury. It's nice, but I'm not sure how much material is there that isn't also in the North Carolina Collection.
I assume you've seen http://www.fmoran.com/frey.html
and _Records of the Moravians in North Carolina_ (parts online at http://www.ncpublications.com/colonial/Bookshelf/Default.htm...
)? I read vols. 1 and 2 of the latter, and I remember seeing Valentine Frey mentioned several times.