This is a known limitation and is native functionality between Domino and Exchange.
Coexistence Manger for Notes does not process any resource reservation requests. Coexistence Manger for Notes calendar coexistence features therefore will work only if resources are homed in Exchange, and synchronized back to Domino as contacts using either the Transporter dirsync or another third party directory synchronization tool.
If Coexistence Manger for Notes will facilitate a temporary coexistence during a migration, note that your resources must be migrated and synchronized first, before you start Coexistence Manger for Notes, rather than at the end of the migration. (This is different from the typical migration scenario using Quest’s Notes Migrator for Exchange, where resources are migrated last.)