Hillary won't win Indiana. She my be able to help John Gregg win though.
Hillary will hurt John Gregg's chances more than help them. John Gregg will win on Pence's negatives. And possibly Trump's negatives.
Hillary is engaging in a 50-state strategy. Which makes sense. As far as the Electoral Vote is concerned, she pretty much has Trump on the ropes. There's no path to electoral victory Trump can spend his way to that doesn't expose another path for Clinton. And if it does end up being a 10-point victory for Clinton, these dollars spent in places like Indiana could yield some pleasant surprises.
And while it won't help Gregg, it might help Democrats establish themselves on the ground, and maybe the Bernie movement unseat Republicans in close districts (2nd, 8th, 9th) in 2018.