Supermicro assembles systems - not motherboards. The MBs are assembled by a third party and this vendor has not been exposed. I suspect its one or more of Foxconn's china plants. Foxconn recently agreed to build a new factory in Wisconsin.
I think my point supports yours. The rice chip story certainly sounds fake. Firmware in old 8 or 16-bit systems couldn't be field flashed. Its been easy since then.
God bless the clockfags
True You still have to decrypt encrypted traffic