The Hilton's garage has actual parking gates but in my experience front desk agents have been very lax in actually posting parking charges to folios. I think out of all the nights I have spent at the Hilton in LEX, I've been charged for parking on only one or two nights.
Just in case anyone hasn't booked flights yet, all three airports (CVG, LEX, SDF) are Citi/AAdvantage Reduced Mileage Award destinations for October:
https://www.aa.com/i18n/aadvantage-p...age-awards.jsp
Remember that Citi RMAs aren't just valid destinations but also origins for the month (in case anyone needs to do a one-way back FROM CVG/LEX/SDF).