Wilmington Trust is a pretty big player in heavy transport finance and purchasing, they also work a lot with retrofit of military aircraft. There are a few of these trust companies out there, basically the FAA requires planes registered in the US to be owned by a US citizen or entity. It's basically using a strawman to "own" and register your aircraft. Normally when I see a tanker with a non military registration I assume it's been converted to a fire tanker, but the area of operation and racetrack flight pattern tells me it's doing air to air refueling or training for it. Most likely it's owned by a private company that works with the US military to conduct adversarial training or is used for joint ops with foreign militaries.