The GeoTIFF, ArcGrid, BIL, GridFloat and IMG formats available from the seamless elevation datasets from the USGS National Map are all recognized by Surfer as valid grid files. You can use them in any place in Surfer that requires a grid file (creating maps, or any of the grid functions under the Grid menu).
Even the GeoTIFF, which is in TIF format, is actually a grid file since each pixel has Z information associated with it. When using the TIF file, you will need to change the Files of type in the Open dialog to either All Files or TIF Tagged Image, since TIF is not included in the Common Grid Files group.
Updated October 25, 2018