Here is a trip advisor link. It looks like they have full hook ups so at least you can run the a/c. Hopefully some of the comments here will help.
https://www.tripadvisor.com/Hotel_Review-g45963-d226775-Reviews-The_RV_Park_at_Circus_Circus-Las_Vegas_Nevada.html
As far as parking in the lot when staying at the hotel, I think as long as you let management know it should be fine. Otherwise they may think someone is boon docking there. At a minimum I would leave a note on the windshield with your first name and room number.