Hello Rob,
Both Translink/Ulsterbus and the people who live in the locality know of Scott's Corner. I doubt that it is the place about which you are enquiring but I'm almost certain that there are a few such places that John Broderick (aka SeanRuad) was unable to include in his IreAtlas site before he passed away on April 7, 2001. Translink/Ulsterbus drivers might know of another Scott's Corner on the Newry - Markethill Road.
I have been in touch with Ulsterbus/Translink who contacted the Portadown Depot to see if they could throw any light on the subject but they only know of the Scott's Corner you found on the internet.
All I can say at the moment is don't rule out the possibility of another place with the same name.
Rosemary Joan, what does your map have on the A28, please

Christopher