So here's the response I received from DL on this issue:
Dear Mr. jjglaze77,
Thank you for contacting us through delta.com. We are sorry for the
delay in responding to your message.
Delta's Round-the-World
award travel can be booked on any SkyTeam or
SkyTeam Associate and Alaska Airlines, Avianca, and Hawaiian Airlines.
SkyTeam is a worldwide alliance of AeroFlot, AeroMexico, Air France,
Alitalia, China Southern, Czech, KLM, Korean Air, and Delta Air Lines.
SkyTeam Associates are AirEuropa, and Kenya Airways.
If you have additional questions, please let us know.
We appreciate your support and trust your future flights will be
entirely satisfactory.
Sincerely,
XXXX YYYY
Medallion Desk
www.delta.com
This information seems to be identical to the rules for PMDL RTW Awards. However pre-merger, the set of airlines: ST + ST Associates + AV/HA/AS was identical to the list of carriers on the "multi-airline" award chart on delta.com. Now, all the PMNW partners have been added to that list, yet apparently they are not available for RTWs? Doesn't make much sense...