I did a lot of testing -- yes, SNB DOFF's work, but their 1% trigger rate makes their proc fairly rare. It took 5 minutes of non-stop CRF firing from my ship before we observed 1 SNB-proc actually happen. After posting the latter, I noticed a lot of Exchange Subnuc DOFF's price-crash from 15+mil down to 2mil.
Is there a debuff icon?
My fleet mate fired on me with chroniton beam bank for several minutes while he had 3 of the SNB doffs on. During that entire time, it did not go off once. But, all of his other debuff procs did.
After 5+ mins, we gave up, as we couldn't see any obvious indication that something was debuffed. There should have been an immunity icon if anything.