Are they paying Docker (the company) for anything? Or just using containers as a part of a wider software infrastructure?

I've been using Docker since early 2014 and they haven't gotten a dime from me. If you count the storage and bandwidth on the public registry I've cost them money.

Is any employee of Docker, inc. critical to your use of containers? Is any copyrighted, non-OSS Docker, inc. code critical to your operations?

Where does the money go.

It doesn't cost money to use the docker format. Why would they get a high valuation from no revenue?