From my point of view it is a good idea, because it enables separation of roles. I understand it may complicate things as well, but that's a price I'm willing to pay. Also, I prefer using non-personal Live ID with artificial email addresses to make them
less dependent on a specific person within the company.
I was also asking because I experienced conflicts between Windows Phone Marketplace and the new Seller Dashboard for apps for Office/SharePoint. I had to use the same Live ID, because internally the two marketplaces share portion (yes, only a portion) of
profile and tax data. That's why I'm now concerned how the Azure Marketplace works not to screw things at first.
So if there are no clear limitations, I try to proceed with Live ID "C" from my example.