By some, for sure. Anything that drapes well below the waist is not a jacket in most parlance.I gifted my father a smoking jacket for his birthday once. He gifted it back to me sometime after he had to stop smoking cigars. I never smoked cigars enough, or in a manner that would merit donning a jacket (usually I was out and about, not at home). But now that I've taken up pipe smoking, I've thought of that jacket again and hope to pick it up soon and try it out.
Also, stylistically, there seems to be a big difference between a jacket and a robe, yet when it comes to smoking both things are called "smoking jackets"?