Does the radiant barrier have to be airtight in order to work?
No; you’re installing a barrier against radiated not convected heat, so you need not cut off air motion. In fact, ventilation from soffit to peak improves radiant barrier system performance. Small tears and holes will not significantly lessen the performance of the radiant barrier, so don’t worry if you must cut and patch around obstructions such as vent stacks and truss supports.
