Benzodiazipines work by binding to the GABA-A receptor and cause a cascading release of GABA. This is what causes the intense relaxation, sedation, and hypnotic effects of benzodiazipines.
Trazodone on the other hand, is an old school anti-depressant - one of the very first to be exact - that executes its mechanism of action through potentiation of serotonergic activity in central nervous system. It is in a class of medications called "trizolopyridines" but structurally does not bear any resemblance to tetracyclic anti-depressants. Its structure and mechanism of action mimic that of an SARI, but it's not quiet the same (as far as I'm aware.)
Trazodone is used now-a-days as an anti-anxiety agent, and as a sleep aid. In addition to its serotonin potentiation, it appears to be an alpha 1-adrenergic receptor antagonist. However, this is not confirmed and is only speculated.
Because Trazodone's hyponotic effects are - probably - though stopping the flow of epinephrine to the central nervous system, I don't see any reason why a benzodiazipine and trazodone would interact.
Keep in mind, however, that I am not a doctor and all my information provided here and on all of my other posts are just speculatory and based off of my own personal research. Be very careful when mixing an adrenergic antagonist with a GABA releasing agent. If push comes to shove and you accidentally take more benzos than your supposed to, the only thing that stops your heart from stopping is the adrenaline in your central nervous system.
If you take too many benzos and trazodone on top of that, you could very easily go into a coma or - in worse case scenario - die of a heart attack.