Even in the dead of winter at MSP, most of my car rentals at the airport have come with all-season tires, even the smaller SUVs. [Most of my MSP rentals have been with Hertz, Avis, National, Alamo and Enterprise.] Even during snowstorms when I've picked up rentals at MSP, there is no counting on regular vehicles there having winter tires. If you have your choice of vehicles on a lot like I do at times, you could go around to see how the treads on the tires are and pick a car that way. Most people picking up rentals don't do that kind of tread-inspection thing at MSP even during snowstorms when I've been there. Just like for my winter car rentals in Europe, I make a habit of tread inspection at MSP and at ORD since the bulk of my rentals in the Midwest are in the November-April period and I'm often driving out in snowy and even icy conditions.

Call up Sixt at MSP and see what they say. Unlike Sixt at various other places, Sixt at MSP had been very good to me since they opened the MSP location. But even if a rental car company says the car has winter tires, I never take their word for it. Tread-inspection is key.