It is not possible to send USB inputs to an SD Card for recording. By design, the USB input is not listened to on the digital send source back to the mixer. This would be a Feature Request.
However, AVB interfacing over a Stagebox (Series III Rack Mixer or NSB Stagebox) or a Mac AVB capable computer can record into the SD Card interface on a StudioLive Console mixer's multi-track recorder. It's important to note that a Mac AVB capable system cannot record/playback audio through a mixer if that same console also is in Stagebox mode (we express that in this article here why), but a single interface to a single mac system enabled can be done.
NOTE: For each channel that you want to record over AVB, the Digital Send source should be selected on the mixer. See Section 2.2.4 of the Stagebox Mode Addendum Manual for reference.
In summary, if the Local Analog inputs or AVB input is utilized, it can record to an SD Card but the USB return cannot.