Supergiant.io works for AWS, Digital Ocean, and Open Stack: https://supergiant.io/tutorials

Which is fair. They are paying for the position via ppc. Companies that are docked for blackhat techniques can still do ppc, assuming they are reputable enough.

While I realize that it involves different business units entirely, but a company paying itself for its own products seem a bit weird to me, doesn't it?

It still costs Google money to run ads, in the form of opportunity cost (they're not getting the money someone else would pay to be there).

The bit about shifting budget dollars around is an accounting issue. many (if not all) advertising businesses have "house ads" that they run for their own products.

It's similar to when you see an ad for an NBC show while watching a different NBC show, or an ad for Consumer Reports auto pricing service in Consumer Reports magazine.