No hydraulic roller cam is made out of billet steel. Only solid rollers. You can use any good quality steel gear or the new composite one's which I don't trust. Your cam spec card should have it written on it the type of gear recommended. Do not use bronze gear with hydraulic cams.
No off the shelf HR cam are on steel billet, though custom ones generally are, comp will grind them on a -9 steel billet if you ask. The composite gears are ok but they do break, they are originally made to run in dry sump race engine where there is no oil pump load. Generally off the shelf HR's are made from selectively austempered ductile iron, which is quite hard unike normal cast iron flat tappet cams.
drill a hole in the gallery plug behind the gear and use a melonised steel gear and it will be fine.