As HPB infers. it's a case of 'consult the flight manual' for each type, although, as often, FAR certificated rotorcraft may have 'recommended' max slopes rather than 'Limits'.
Control power, available cyclic stick movement (esp. in some relative winds) C of G and undercarriage configuration all play a part.
Generally, skid equipped aircraft are easier than wheels. If tricycle wheels are fitted, a nosewheel lockpin is highly desirable, as on SA330 but not on B412 wheeled kit.
The dear old Wessex needed a firm touch, so as not to excite ground resonance.
Aircraft with rigid or semi-rigid rotor systems require great care not to impose high mast bending moments, so in-slope cyclic use will be limited, nothwithstanding available control displacement.
Some helis may be landed nose down slope: Chinook, for example. (But left to its own devices it doesn't know back end from front anyway: try it AFCS off on instruments!)
If you've got appendages like TV/FLIR turret additional limits to the basic clearance may apply.
Hope this adds a bit.