Does the DS Series decoder reject transmissions from the CMD-KEY#-fff with all address lines pulled to GND (default setting)?

Yes, the DS Series rejects existing Linx CMD-HHCP-fff, CMD-HHLR-fff, CMD-KEY#-fff and OTX-fff-HH-KF#-HT transmitters where the addressing is set to the default all OFF (or ON) state. This is intentional, to eliminate triggering from unintended transmitters.