If you use the “–checks” option, you will ignore the scan function. This means the scan function cannot decide if your device is a Dell Powervault.
Can you post your “snmp_scan_function” and the content of the system description & object OID?
For the Powervault ME4 i wrote last week a special agent for the well documented REST Api.
If all goes the right direction i can upload this mkp to my github the next days. Then you can test if it is working with your system 