modern cars should be ok with 10% ethanol as most are designed, especially American cars, to run on the gasoline formula offered here. It's hard to find gasoline that do not contain ethanol thse days.
The problem arises with old cars that wasnt designed to run on ethanol and the ethanol interacting with fuel line seals that wasnt made to be alcohol friendly causing leaks in fuel system.
06 DTS should be fine. Granted, though you might notice a slight decrease in MPG as ethanol is not as efficient, although cheap to make from corn, as gasoline per power stroke of the engine. Take note though, unless it specifically says so i nthe owner manual, which I dont recall it stating the Cadillac DTS manual, DO NOT USE E85 (85% ethanol). But more than likely you already knew that but i have heard of that happening and it caused lot of headaches and a smiling mechanic as those Northstars are not cheap nor easy to work on compared to usual American motors.