My understanding is that the term "rogue-lite" came about sometime around / after the Berlin Interpretation of what it means for a game to be rogue-like was agreed upon. It's called the Berlin Interpretation because it was discussed during the International Roguelike Development Conference in Berlin in 2008.

So, Diablo and Diablo 2 being released in 1996 and 2000, they pre-date at least common usage of the term "rogue-lite".

edit: see http://www.gamesofgrey.com/blog/?p=403 for a critique of the Berlin Interpretation as written.