This issue is fixed in Oracle Hardware Management for Oracle Solaris 11.4 SRU 1.

For some Oracle SPARC systems, such as the T series and M series, the fwupdate list and update commands might not work with Intel-based network controllers after performing a hot plug of a controller device. For example, after a hot plug of an Intel-based network controller, if you run the fwupdate list command you might not see any Intel-based network controllers listed. If the fwupdate command cannot list the details of a device, it cannot update that device.

Workaround

If you encounter this issue, you need to reboot the server in order for the fwupdate command to see and list details of Intel-based network controllers in the system.