what gear for hydraulic roller cams?

As others have stated... It all depends on the cam core material. Typically you will get a Billett/steel core...or an iron core...
With billet/steel ...you have 2 options, bronze or melonized/coated steel.
Iron core uses a regular stock style gear. Easy.
Billet/steel..Crane sell a coated/melonized gear. They are not to be used with a used cam , they are a one off..must be a new core/machined and can only be used on the cam they're mated to. Like piston rings, you dont reuse them and you dont switch holes with them after break in.

Bronze to some extent ends up in the oil and magnets don't grab it.
Fwiw the last hyd roller from lunati I bought was billet/steel. It will look smooth between the lobes...even blueish.
I recommend the melonized gear/"crane coated steel gear" as its labeled on the package. I run one.

Good luck.