Looking at the google Map of Universal Studios Florida and Islands of Adventure, they appear to be linked by roads/pavements on the backlot.
Would it be possible, to have IOA and USF linked together through the backlot during Halloween Horror Nights, Houses/Mazes could be placed in the dark backlot area and parts of Islands such as Jurassic Park and Poseidions fury could be opened during Halloween horror Nights. While areas of the park like Harry Potter and Zeuss Landing that cannot be used during Halloween horror Nights remain closed off.