Yes, it is true. I'm not completely sure, but I think it's 10% off for the value hotels, 15% off for the moderate hotels, and 30% off for the deluxe. I know it is 10% off for the All Star hotels and 30% off for the Contemporary and Grand Floridian. I don't think you get a discount at the Poly; if you do, it might only be 10%.
Hope this helps!