This KB tells you what OS Flavor / version the MVM SSH Module can authenticate to.
Your other question is a little more complex.
If you go to scans / new scan. Choose the Shell Advanced Scan Template
Then go to the Settings Tab, Vuln Selection
Then look at Vuln Selections for the following 2 categories, it should give you an idea about how many Cisco checks we have that require credentials (Both the following categories require credentials):
Cisco IOS Patches and Hotfixes
I hope that helps!