This Knowledgebase article details the reasons why the Data Rollback Module (DRM) should not be scheduled to take shadows while backup or an offline maintenance task is running.
Why Neverfail recommends the DRM not be running during backup?
The Data Rollback Module itself is a backup mechanism. It creates a copy of the protected data that can be later used as a restore point. While performing a DRM snapshot, the server I/O load increases by the amount needed for DRM to perform its copies. Concurrent backup procedures can lead to very high I/O load that can cause the server to be unresponsive.
Please refer to the following Microsoft article for further details:
Why Neverfail recommends that DRM be turned off while offline maintenance runs on the Exchange databases?
Regular maintenance shadows should be switched off in order to avoid taking snapshots of data that is in an inconsistent state. A manual snapshot of the working system should be taken prior to performing the maintenance. This way all the data will be safe in case the maintenance causes any errors.