In order to monitor ASM, are OS credentials optional?
If it is optional, what additional monitoring is available with OS monitoring?
The OS is used only for the alert log monitoring. All the ASM Disk Groups and ASM Disks information (storage, performance, etc.) is not being retrieved via OS but rather the Oracle ASM agent accesses dynamic views from the ASM instance connection (V$ASM_DISKGROUP, V$ASM_DISK, etc.).
The only issue when installing ASM agent without OS collections enabled is that the ASM agent will be unable to monitor the ASM alert log messages.