Can gestational diabetes be dangerous if you have meyloproliferitive disorder?

No more than usually: Chronic medical maternal conditions can predispose to gestational diabetes mellitus or gdm (either inherently or due to their medical management), but should not alter the significance of gdm once diagnosed. A myeloproliferative disorder could presidpose you to pregnancy complications as well. I can only think of infectious scenarios in which the two diagnoses would potentiate each other's effects.

Yes: Gestational diabetes can be dangerous with or without myeloproliferative disorder.