If you're hosting the event at Hard Rock Live, why would you be able to walk around backstage at Universal Studios? The Hard Rock Live and Islands of Adventure share the same backstage areas, with some of the Universal Soundstages being adjacent to the Hard Rock Live. However, if you do not have any sort of ID that authorizes you to be backstage, you will most likely be escorted out of backstage, or even the park, by security.
(Soruce: I am a UO TM)