If there were indeed skulls made as gifts at some point, following the release of the film, those would be classified as replicas as well. This was just something I was told, so I have not verified it.
I could not personally match the skull sold at auction to any images in the film, The Terminator, and The Winston Effect book makes no mention of any metal skulls made for the film. Those shots in the film that I made HD screencaps from - there are a number of differences between the skulls seen in those caps compared with the skull offered on eBay.
Given the budget restraints of the first film, I can't think of any reason why there would be such significant differences between any two skulls made for the film.
Jason