I read somewhere (link lost in 1Gb bookmarks) that RDM is difficult if not impossible on the Teensy hardware due to the timing required to send RDM in the space/time after dmx512 main message. You need to receive and send on the same port, sending within the proper time slot of the protocol.
That, and running out of time b4 jumping into a production gig, put a stop to my DMX explorations.
Seeing the FlexIO announced under Teensyduino 1.54, i wonder if there are hooks now to do the proper magic.
(Gig was installing led neon for vapid reality tv show. got to work with 24v leds, long runs etc. Paid well, but hard work under Hawaii sun.)