Is it true that you should connect the isolated ground of a dc/dc converter to the non isolated ground by a resistor(1k, 10k, 100k, 1M, 2M2) depending on your application so that you dont get static voltage to grow between the 2 grounds?

I really do not know, never did, however the theory sounds interesting, at least if you use the megohms.

If you do so, make sure you use a resistor that is large enough (physical size) that no sparks can jump.

Erik