Not the ones I dealt with! The screws were alloy. Dzus were steel, but the cups were put on with alloy rivets (we didn't use very many, either). Even the nut plates on "blind" assemblies were alloy. What little steel fastners we DID use, were plated, zinc primed, and painted, and the nut plates on "blind" assemblies were alloy. While SOME assemblies HAD to be steel, they were primed, painted, and installed with neoprene or caulking to prevent dissimilar metals touching.
That said - corrosion is a BIG concern onboard a ship. ANYTHING that can be done to protect the ship and aircraft is WELL worth the effort! It's a NASTY enviroment. That's why sailors are taught to paint in boot camp! LOL!