when you say "employee rate" - do you mean the rate the employees of Hilton receive or the employees of your client receive. I sometimes use my clients corporate rate because they have a better negotiated rate. I just call up and say. "Hi I am prncess674 and I am an employee of [insert client's name here], we have a negotiated rate of $XXX I would like to check in on XXX."
Unless your client is Hilton I don't think you are getting a Hilton employee rate.