Right now, I use the combined view/proj matrices generated from the engine for culling. I'd like to move the matrix generation up to script, where the HDRP explicitly controls the matrix gen.
As far as shader constants, this affects the usage of:
_ViewProjMatrix (not used the same as UNITY_MATRIX_VP in stereo/shadows)
_ViewParam
_FrustumPlanes
These three are used in GetTessellationFactors.
_InvProjParam (unused for now anyway)