No IMD, its not on the FCC RADAR. They only care about out of band harmonics, case emissions and operation (positive gain) in the 26-28 MHz band.
Case emissions is strange. They must think we don't use antennas.
If that's the case, Andy Leimer at the FCC who wrote me the earlier correspondence must be all wet, as he stated they do measure IMD. I wasn't sure about that, and now there's a disconnect. I should probably ask somebody else at the FCC.
Re the case emissions, that does seem weird but I think that wasn't intended to address in-band emissions. Some amps do have microprocessors and stuff in them (in fact, any certificated amp to meet the 26-28 MHz lockout requirement would need to have a frequency counter in it, as I can't think of any other way to do that and still allow operation on 10m), and that stuff might have case emissions that are way out of band.
I don't like amp designs that are "too well" shielded, myself, they're just a PITA to service. Even the SB-220 has way more internal shielding than makes sense.