If QuickBooks backup is running when CISM starts a new sync: 

QuickBooks will deny CISM access and CISM will get an error... BUT, the next time CISM runs a sync, it should work (assuming the QuickBooks Backup has stopped by then).  

If a CISM sync is running when a QuickBooks backup starts up: 

QuickBooks Backup has priority to the QuickBooks data and CISM will get an error. But again, the next time CISM runs a sync, it should work (again, assuming the QuickBooks Backup has stopped).

The bottom line:

CISM should not interfere with the backup, but you may see errors on the CISM screen.  However, once the backup stops, CISM syncing should start up normally.