It’s just that my idea of what it means to use someone includes more overt immorality, i.e. deliberate deception of the person being used in a dishonest attempt to gain some value.

But if all that is meant is that Mr. Elton uses Harriet as a subject of conversation to interest Emma, I would not try to argue that he doesn’t do that. I have little doubt that he'd blather away about Harriet if/when/for as long as it appeared to please Emma that he do so.