Krugman has a very full bio so you can find all sorts of things there, he hasn't hesitated to work with anyone willing to listen to his opinions and expertise.
EDIT: I'd also suggest that as a default with the participants in this particular disagreement, anyone with self interest at heart should probably think about siding with Amazon. Jeff Bezos doesn't lose too many fights.
You can check out some of Krugman-the-journalist's most notorious contradictions here: http://wiki.mises.org/wiki/Paul_Krugman#Contradictions
That's a very different thing to any suggestion he might be part of an orchestrated PR move by Hachette which was the original implication.