Most 275/65R20 tires are rated/tested for 7.5-9.5'' wide wheels (check the specific brand, model, and size for its exact wheel width range), as others here have stated.
They can be mounted on a 20x10, but the tire will be slightly stretched and the sidewall will be under a little stress. Might not ride too well but you'll get brownie points from the Euro and JDM guys for the hella flush stretch and poke stance. Not my cup of tea at all, but a lot of show trucks have stretched tires as well.
Picture below is an extreme example, I think the tire width and wheel width delta is almost 2'' hahah...