Epic is famous for lock ins - once you pay the $50-100 million contract for them to take over your IT, your data will not interface with any other system again, ever.
I'm not too familiar with MUMPS but is there anyway the hospital's IT Dept. could allow a 3rd Party App to integrate to the actual MUMPS database/data source to get to the data, and thus bypass trying to get access to the EPIC/Cerner API or HL7?