After a number of calls with KLM, Flying Blue, and AmEx Netherlands I have come to the following conclusions:

- it's nearly impossible to book domestic Delta flights with KLM;

- level miles cannot be earned on any purchases from Delta, even if the 'stock' is KLM - it has to be charged by KLM;

- if you can find a domestic flight on Delta in the US with the KLM booking phone center, it'll be much, much more expensive

- this entire process is a big waste of time;

So there you have it, fellow intrepid benefit maximizers and SkyTeam friends: forget about level miles on Delta.