What is most likely, is that the LED strips are split into smaller lengths with individual power supplies and drivers. These will be individually addressed at the smaller intervals, meaning there isn't actually anything split over two universes.
As for patching and mapping these, it depends if the control units have been addressed in a sensible order. If it goes along one strip, then along the second strip, and so one... then creating the largest fixtures that fit within universes and don't go above the highest address on each strip.
If it has the first section of the first strip, then the first section of the second strip... then you only need to create a single fixture, but mapping becomes more laborious as you've got to position so many more fixtures.
This should have already been worked out by someone either within lighting or video, as they'll be designing any data runs necessary. So send an email back to your contact asking for the details. If they haven't already provided this detail, then they may not be intending for it to be used for visuals.
If you're the only/main VJ for this festival then it's probably worth trying to get this working, but if you're only on for an hour or so then the time spent making it work may be better spent preparing your content/composition.