One thing to bear in mind is that indie game developers do not have a large budget, so they are generally unable to pay for large scale marketing. While that large of a fanbase can certainly be monetized, as a Twitch Partner and otherwise, there is something to be said for showing new and fresh content from indie devs as a way of entertaining your viewers and showing them something they haven't seen before.
It also bears mentioning that you can't promise the developer you partner up with that your audience will be responsive to their title, i.e., "For x amount of money, you'll x in sales because my fan base is x number." The best publicity for an indie is spontaneous publicity, rather than a "buy my clicks" scenario. Paid advertising, which you generally have to disclose as such, doesn't tend to appeal well to audiences because you have to say "I was paid to endorse this game, so I love it!" That tells the viewer straight away that the review is going to be biased in favor of the product, rather than an off-the-cuff experience from a streamer picking up a game and never having experienced it before.