I'm not a metallurgical Engineer, but an Engineer, so here foes.
These are made of a Chrome Steel used for ball bearings. The chrome content is 1% or so, and the carbon content is there to make it hard and tough for the high bearing loads.
Stainless has 10% or more Chrome. 304 SS that most of us have in our set ups is 18-20% chrome so the it is "rust free".
With the lower chrome content it may be best to put one in a glass of beer for a week or whatever length you will dry hop with and see what happens. If it comes out pristine then you are good to go, if you see corrosion then you need a plan B. I use some 304 SS elbows and nipples that are not in use for my dry hop weights. I also have some glass marbles that are also used.