It depends what your $500 rebate is. There are sometimes regional offers that are separate from National Offers. Simply ask the dealer for a copy of the official program rules to show you that it ends today. It probably does, a lot of times Manufacturers will have a rebate at the beginning of the month to drive sales early. It's a dealer Psychology trick. Normally a dealer might sell 10 by the 20th of the month, a typical dealer will double that the last ten days, efectively selling 20 that month. If they have a rebate early and he sells 12 by the 20th his mindset is still around doubling that number, so he'll sell 24 that month. Which means it cost them an extra $1,000 to sell 2 more Jeeps per store, multiply that by a take rate, because not ever dealer will sell 2 more, and there you go, an incentive that drove more sales.
In a nutshell, they are probably right, it probably does end today. If it's compatible? Again we would need to know which rebate. I believe you can call 800-227-0757 and that is program headquarters for rebates. You would have to tell them your Zip Code and they should be able to pull the regional and national offers.