DT and Wheelsmith 14gau spokes and nipples have different thread pitches. They are not interchangable- at least this is the way it was for years and years. Maybe that's changed in the past couple years?
Stainless steel spokes are very resistant to water and moisture, more so than galvanized or chrome plated spokes. A DT or Wheelsmith or Sapim spoke use a slightly different stainless material and will be more water resistant than Taiwan or china stainless material.
The black spokes from DT, Wheelsmith and Sapim are stainless to begin with. The black color is electro-deposited or chemically etched, or something like that. It's not going to give you additional corrosion resistance. It's substantially more expensive though.
If you are riding through a lot of salt water and leave the bike outside all year round, expect your stainless spokes to get a very light layer of surface rust on them which can be scotchbrighted off. That's normal. it does not mean the spokes are defective or that user error contributed to the 5 microns of rust growth.