But you are driving that DCDC with a 13v supply? so presumably already have some HV isolation upstream?
If you have say a fixed transformer, then the HV winding is wound onto the same physical location as the secondary, and so high levels of isolation voltage are sensible, but driving an isolated LV module, hmm im not so sure? (because it would take multiple failures to cause a breakdown)
But, it's your product, you need to evaluate the risk / hazard and set appropriate levels, and provide suitable matching engineering solutiions