So important! A good orchestrator can create something truly special onstage and a bad orchestrator can make the sound designer's life a living hell.
It's paramount, as a Sound Designer, to approach any new collaboration with care and respect, and working with a music department is no exception. Different music teams have different internal structures and rules - what falls to an Orchestrator on one project may be the work of a Dance Arranger on another project. As you sniff out who does what within a given group, you may notice similarities with previous collaborators, or you may discover hitherto unknown methods of working. No matter what, though, if your opinion is to be trusted, or even vaguely considered, you must give the music department the same respect you would ask for in return.