I've done quite a few rides from Harrah's and never had any problems. I usually park on the overflow parking which is on the South end of the property. In return they get my business - I eat lunch at the casino and when I feel lucky, I throw a few bucks in the machines. And I always do this in my cycling clothes, so they learn that we are customers too. As opposed to the taco shop on the corner of Valley Center and Hwy 76 - I wouldn't buy even a bottle of water there.
I think the casino is actually pretty friendly towards cyclists. When they had the Tour of CA up Palomar, the casino offered free parking for the spectators.