Yes it is, of a kind.
Does it make a difference? Well it rather depends but on the whole I have found that upscaled DVDs do give some noticeable improvement.
HD TV can sometimes be upscaled rather than true HD, ie recorded in HD. When viewing HD TV (Sky) I have found some of the recorded material obviously SD and upscaled but other programmes sensationally good. The live sports programs are outstanding.
So, upscaled seems to fit (to me as an observer) between SD and HD.