>> but I think it's reasonable to assume that they also need to stay in Microsoft's good graces (since MS make the awards)

Not actually true. There have been MVPs who were vocal against MS products, even the products they were MVPs for! There is no obligation on MVPs not to criticise Micrsoft.

Just think about the huge outcry when MS said they were terminating the MVP program!
As I heard it, one department in MS got cold feet about possible legal issues if an MVP offered incorrect or misleading advice - and that seemed to have been translated through chinese whispers to "we'd better canecl it" just in case there was an issue.
From the number of emails that hit mailboxes of various MS executives, most of them critical of MS for that decision, they got the message. And those people are still MVPs.
Now, if sending a critical message to Steve Ballmer doesn't get you struck off as an MVP, I think the worries are unjustified.