Painting would be for cosmetic reasons, to make it match, but not for the purpose of preventing corrosion. Yes, it would be needed to be treated to in order for paint to adhere to the galvanized metal.I didn't know about the paint on galvanized metal. I'll have to read up on it. I don't think any such treatment was proposed. Thanks!
One of the simple treatments for galvanized metal is just vinegar and water wash and then properly drying before painting.
From the description on your first post, this sounds like a fence that would be front and center, so I would expect that painting would be desired.