Rolexes, at least the trip lock, have a gasket that will keep water out even if crown is unscrewed. At much shallower depth than what watch is rated to obviously. Are Omegas the same? I know the HE valve will be okay left open in 10m of water I think Omega said?

 

Was always told up to 50m for the Planet Ocean, if unscrewed yes. But that's assuming it's not in dire need of a service of course

 

I know that the SMP is waterproof even with the crown unscrewed.

 

Nothing changes with regards to the seals in contact with sealing surfaces if the crown is screwed down or not.