Head brewer from Lagunitas thought that the breweries for the Big 3 are so specialized to their specific product that they probably couldn't produce a beer like his even if they wanted to. Now they do have the financial resources to build new breweries of course and they actually have some very talented brewers working for them. But for now they are sticking with marketing gimmicks and an inferior craft beer lineup (excluding GI).
When InBev first purchased GI with a "hands-off-brewing" contract in place I thought it might have been a step in the right direction. Having the Big 3 opening up their resources (political, financial, distribution and technology) could be a huge benefit to the craft beer scene, while allowing the Big 3 to get a piece of the action. Turns out InBev didn't give two shits about GI and what they were really hoping to do is create a loophole in Illinois liquor laws which would have allowed them to self-distribute Bud there (in state breweries can self distribute, out of state ones can't). By being able to self-distribute Bud they could undercut Miller/Coors and make way more cash that way than GI could ever hope to bring in. But that has been InBev's m.o. Preach for the sanctity of the three-tiered system then through political maneuvering they create ways that allows them to operate in multiple levels of it.
Even if that plan doesn't pan out (the whole thing has become a tangled mess in the IL courts) they still control all the new distribution for GI and as outlined in the article above, they plan to utilize the GI product with their ability to operate on razor thin margins, thanks to their sheer volume of sales, to start starving out some of these craft breweries.