Bootable USB media is supported for SPARC in addition to x86 systems. You can use bootable media for stand-alone system installations that do not use an automated network installation. You can create USB media for SPARC using the Oracle Solaris Distribution Constructor. Additionally, installation images can be copied to USB media by using the dd(1M) command (or its equivalent command on other platforms) in addition to the usbcopy(1M) command.
See the Oracle Solaris 11.2 FAQ for more information on using usbcopy or dd.