Technically, no. Parking for dining is restricted to a couple of hours.
If you're staying at a WDW resort and parking at the Poly for a meal and then leaving the car in a lot, there's a good chance (likely, but not guaranteed) that Security will not care. After all, it's not like you're screwing them out of a parking fee by parking at the Poly versus the TTC, because people staying onsite get free parking in the theme park lots anyway.
What would make them more likely to enforce the "don't leave your car here" rule is if the lot is so full, guests who are staying at the resort are unable to find a spot. Let's face it, if you're paying the dough-re-mi to stay at a Deluxe resort, it's really not fair to be unable to find a parking space because someone staying at a moderate or value resort decided to leave their car in a spot you should be able to access.
So if the OP does it (and if the OP is staying in a WDW resort), it's not likely your car will be towed or disabled, but it's not a sure thing you will be fine either, and you can't feign surprise if your car's not there.
However, if the OP is not staying onsite, and by using the Poly lot you're avoiding paying a parking fee, the odds of there being a problem would probably be higher.
One way to potentially avoid the issue - when you go to the Poly, pay for Valet parking.
