Don't you have some sort of SAN / disk arrays in your case?
Having any physical disk attached to a physical host is quite rare in enterprises nowadays.
Smart data can be accessed only by privileged users and oneagent plugins run as non privileged user. So you have to deal with this limitation and use sudo (Linux) or some other alternatives.
Yes, there is a SAN, but there are local too. You are right about smartctl, and it might be a challenge. I'll have to think if I go that route. Another idea I'm imagining is getting the data from the logs.