The use of grease holes is probably more related to the cost of the rifle, rather than to an either/or between mountain vs. flatland people. In lower income areas where cash was scarce and moderately priced rifles were made without patchboxes, grease holes at times were used as an alternative...and low budget rifles were made everywhere. West of the Alleghenies, that could occur almost anywhere and was apparently a more accepted practice than back East.
Hill-county people in general were in poorer areas and often had plainer rifles...so there were probably more grease holes used on their rifles. But I have seen plain rifles from other areas, well removed from the hill country, with grease holes. One example is Joseph Blair of Russellville, KY, out in the western part of the state. He was a major gunmaker with a large shop, but made mostly plain, iron mounted rifles. Great stock architecture and molding lines were his primary enhancements. I have seen several Blair rifles with rectangular grease holes in the butt...but have yet to see a patchbox on one of his guns.
A related question of similar interest is....how many gunmakers actually put original grease holes in their new rifles, since I believe most were added later. The Gillespies of NC and GA come to mind with their attractive, egg-shaped grease holes of uniform size and location in the butt. However, I think the number of gunsmiths who put grease holes in their new rifles is rather limited...can't think of any others right now...what about the rest of you? Shelby Gallien