Does it even matter? RPGs need a story and role for the player to fit in. I'd call dota an RPG if we see people actually playing in character, thinking and chatting like how the hero in question should be doing. I only do that occasionally, and only if i get techies. It's fun yelling DON'T RUN, WE ARE YOUR FRIENDS when you're going at full speed with a haste rune towards a target who knows it.

Otherwise, I'd consider dota an RTS. A dumbed down version for players to micromanage sure enough, but still more of an RTS. You have resources, you have units (allied, forest, dominated/summoned), a base to take care of strategically. Really doesn't feel like an RPG to me.