I can't say I know enough about it to say either way, in the article Carmack says:

Technically, the Microsoft tool only performs local analysis, so it should be inferior to Coverity’s global analysis, but enabling it poured out mountains of errors, far more than Coverity reported. True, there were lots of false positives, but there was also a lot of scary, scary stuff.

According to a very insightful, but perhaps now slightly old article (http://cacm.acm.org/magazines/2010/2/69354-a-few-billion-lin...) Coverity tries--for political reasons--very hard to keep false positives down, very much at the expense of false negatives.

Having seen Coverity's results, I would agree with that article. Particularly cogent are the social problems and how they play out.

I'm pretty sure Coverity has multiple "tiers" of analysis, with the initial tier being the subset they're most certain of. Once you fix most of the obvious, almost-no-false-positive type stuff, then they're ready to show you the next tier.