I don't see why not - they are all owned by universal and all quick service.
You are buying the pizza so I don't see an issue.
Going to a full service like Atlantic would be different.
BTW: I see no shortage of people taking donuts from Voodoo and then eating them at the Today cafe in the park - not even buying anything from the Today Cafe and VooDoo donuts its not even Universal.
More than once I got my coffee at Starbucks and got the Focaccia sandwich at Windy City eats and sat outside Today Cafe and had my breakfast. IF the place was full I would not do that but it was not so I did not see an issue with it.