According to the Park Reopening FAQ, fully vaccinated adults from out-of-state may visit Universal Studios Hollywood with proof of COVID-19 vaccination and a photo ID. Here is the information from the Universal website:
New government guidelines now allow us to invite out of-state visitors who are fully vaccinated for COVID-19. Proof of COVID-19 vaccination and a photo ID must be presented at our front gate tickets booths prior to purchase. Acceptable forms of proof of vaccination are a vaccination card or photo/digital photo of vaccination card (including name of person vaccinated, type of vaccine provided, and date last dose administered) or documentation of vaccination from a healthcare provider, in each case showing that at least two weeks have passed since receipt of the second dose in a 2-dose series (e.g., Pfizer-BioNTech or Moderna) or since receipt of a single-dose vaccine (e.g., Johnson and Johnson [J&J]/Janssen).
Out-of-state visitors are not able to make a reservation prior to their arrival at the ticket booths. Vaccinated out-of-state visitors who purchased a ticket prior to or during the park’s closure may also visit but must provide proof of COVID-19 vaccination at the front gates.
Unfortunately, children under the age of 16 from out-of-state will not be able to visit Universal Studios Hollywood. The government guidelines require out-of-state visitors be fully vaccinated and there is no exception for those under 16 who are not yet eligible for the vaccine.