@taprik,
With the Teensy as 'Master', you can control the transmission rate and sequence. If you turn off ACKs, that is the only local transmission going on, so RF interference should not be a problem provided you chose a "quiet" channel to operate in.
A simple protocol of not changing the last received command until you get a correct CRC packet, with repeats of last command in the allocated time slot will work around not using ACKs at the expense of occasional slight delays in response.