Hydraulic and mechanical lifters require different cam profiles. When I did get reground cams, machinist needed to know if cams were to be used hydraulic or mechanical lifters so he could grind them correctly.
With mechanical lifters cam needs to first take off the slack between cam profile and lifter, that's why there is period when lift increases slowly until cam and lifter make firm contact and only then cam profile starts really to push lifter. I think hydraulic lifters are not as fussy because they have some damping built in in form of fluid and the cam can start pushing lifter more aggressively.
I guess if you run mechanical lifters with hydro cam, initial cam profile might be bit too aggressive and cam noses hith lifters bit too hard and cause noise.