From a health point of view is nothing wrong with dosing DMT together with benzodiazepines. It may pose a risk if you take a MAOI, so you should not attempt ayahuasca, pharmahuasca or changa. Benzodiazepines will, however, greatly decrease the effect of any psychedelic.
Generally, a benzo is what is given from health professionals if someone experience a bad trip. Not only because it decreases anxiety, but also because it will decrease the effects of the psychedelic greatly. You may not be able to break through while on benzos.
I therefore believe that you should refrain from taking any benzo before or while on any psychedelic, except if you really want to decrease the effects. Again, note that not only the anxiety will be decreased.
I have moved this topic from "Pharmahuasca" to the subforum about health and safety. Pharmahuasca is an ayahuasca analog where you use pure DMT and pure harmala-alkaloids.