with a 0 offset they roughly sit flush with the outside of the fender, which is what your spidertrax are accomplishing for you. additionally, with them being wider they will protrude inward and outward further, as gaterose stated, which could cause rubbing issues but its hard to say.
i would see if your local discount tire or the like carries pro comp (don't think discount does) or something in the same size, width, backspacing etc and have them throw one on to get a better idea. 9" is a whole 1.5" larger than oem so factor in 3/4" on either side of the hub. you may need the spidertrax to clear them on the inside of the wheel, which in turn is going to put your rim pretty far "out."