The EU has extradition treaties with the US.

Do extradition treaties cover forcing diplomatic planes to land with no evidence aside from rumor that a person of interest is on the plane?

From what I remember Assanged attempted to get diplomatic license (become a diplomat for, don't know the technical term) from Ecuador but did not. There he can't get in a car and none of that stops the cops from setting up a large traffic jam till said car runs out of gas and assange has to walk. I'm not sure if there is diplomatic immunity for a tow truck.

The image of Assange trapped in an out-of-gas diplomatic car, being towed behind a beat up truck driven by a very amused blue-collar driver on the way to the airport sounds rather like something from a Douglas Adams or Terry Pratchett novel.

Since these extradition treaties are not public record, all we can go on, is events. So apparently, yes.