The wheels will most likely NOT have the all important offset required to clear the FWD hubs and still stay inside the wheel wells. Also, the actual hub centers are a critical measurement besides the bolt pattern.
Yeah, I think it'd work. Both vehicles are FWD, so you should have close to the correct wheel dimensions. I'd take a wheel off your Deville and do some loose measurement comparisons between that one and one from your Monte Carlo. If they're close, bolt one on the Deville and check it out. I'm guessing it'll be a perfect fit.