I'm assuming your "diazo-based product" is a design for Plone. The answer is that yes, that product can override the cpt, and the best way to do that is to use z3c.jbot.
Diazo in itself has no possibility to override templates. It works purely on the HTML that the template renders to. But there isn't any problems in including both a Diazo-based design and other features such as template overrides in the same product.