ok.. for now heres what comes to mind...

How can I assure that if even one of the machines has two nicks to communicate with DEV and PROD, that no communication would be routed from the DEV DC to the PROD network?

I was told a simple no, you cannot install a DC in a back network if this DC communicates with machine that are also on the PROD network because there might be some routed information from the DC to the PROD environment.

So I would have to assure, give proof that the preceding is untrue.