Well, I've confirmed JMRI is sending the right addresses to the EasyDCC. Now, I wonder why they don't result in the same packets going to the decoders as when controlled from the EasyDCC plug in throttles? Using the plug in throttles, I have control of locos with addresses above 1000. With WiThrottle though JMRI on the RPi, I don't.
JMRI to EasyDCC addresses from the raw data, following a prefix hex C. For example C1 5D 3F 80 23 is Speed = 0 to loco 349:
349:??? 15Dh
901:??? 385h
1003:? 3EBh
1477:? 5C5h