Does Redundix support the STL firmware ?

Limited.
Redundix is unidirectional IP transport system to transport data from A to B.

The audio from the STL devices can be transfered via Redundix with additional redundancy to make the stream more reliable over Internet.
But the Barix STL firmware can exchange even state information (e.g. about digital IO state and connection state) between encoder and decoder.
When this state information, the Keepalive message, is enabled in the setup of the STL devices (under STREAMING) then it is exchanged bi-directional.

So when the STL is used bi-directional with two pairs of Redundix, then no problem, then even the Keepalive can be transported to the remote site.

But when the STL connection is made uni-directional only with one pair of Redundix, then the Keepalive can be not transported back to the encoder.
In this case the Keepalive should  be disabled in the setup (on both sites) and only the audio stream should be streamed over Redundix.