I was talking with my grandfather when we were on vacation in Udaipur and he said something along the lines of how there were no Aryan invaders. This sounds like Nationalist hokey but is he at least part right? Is the Aryan invasion theoretical, or at least exaggerated by modern historians? Really I want to know to what extent Dravidians or pre-Aryan groups influenced Indian culture.
Depends on the context. If he's saying that Aryans were indigenous to India, then that is not correct.
The Aryans were a gradual migration and comprised a linguistic not a racial group. they came in waves, not in an outright invasion through different entry points. There was no Aryan state, or organized invasion of the subcontinent, but rather, a migration. Romila Thapar is your friend when it comes to Ancient Indian history!