Rebates generally stack, and are a way to help pay for the car, whatever price you may have negotiated with the dealer. Think of it as a $500 check from Ford to you that you can sign over to the dealer when you're taking delivery, reducing the amount of your check by $500.
Financing offers usually come with an either-or rebate: $1500 or 0%, etc. This tells you they cost Ford about the same, and they don't care which you pick :) Again, the cash rebate is just a check to you; you can essentially sign it over to the dealer to help pay for the car. (Which is what people normally do; if you really insisted, you could probably get a check in the mail.)