the snmp settings for each device are configured both on the device and in IMC for each device.
First configure snmp on each device.
Then in IMC "Resource" menu, on the screen for each device, on the right under "configure", set and then test the snmp settings to match what's configured on the device.
This allows IMC to read all the data from the switch, which includes the frimware version, along with all the operatiing statistics. The device model will show a model number instead of just ICMP
That information is stored in the database used by IMC and the report then pulls that data from the database.