Even though I'm no fan of Microsoft and Halo, I honestly can't see how this is as disgusting as some are making it out to be.
It's not uncommon for product placement tie-ins separate from the main product to go around. As long as the main product isn't negatively poisoned by product placement, then why is it a concern that Microsoft isn't "respecting the brand" and making little tie-ins for extra cash? If the main product starts to get negatively poisoned, then that will definitely be a cause for concern. Until then, this is just another silly marketing gimmick that they're doing to get people to buy Halo or Mountain Dew/Doritos, and can be ignored by Halo fans.
Nintendo's done product placement in side projects. How about the special version of Mario on NES based on the Japanese TV show "All Night Nippon?" I think Wave Race 64 and 1080° had tie-ins with Kawasaki and Tommy Hilfiger (those also had a presence directly in their games, but minimally). Those have not had a negative impact on their main games.
If there's someone to give a critical eye to, I don't think it should be at Microsoft advertising their game with popular snack products, but at any game reviewers who also fall into this advertisement scheme and whose opinions may be swayed. This is largely bad timing with the whole journalism ordeal.
So no, I can't see how it's so disgusting. Maybe I'm missing something, but it seems pretty standard to me, and yet still better than what movies/TV does sometimes with blatant product placement in the middle of viewing.