It is definitely open.
Just came back from LAS yesterday - stayed at Paris (not Harrah's). They were doing some upgrading at Harrah's pool, but it is open. Of all the Caesar's Entertainment properties it is the least glamorous. If you are staying during Mon. - Thursday, you can use the other properties pool - not as convenient, but a nice amenity.
Get an answer from Harrah's Las Vegas staff and past guests.