The snow LOD and ash LOD shaders are applied onto object LOD in-game.
They do not affect LOD generation and xLODGen or DynDOLOD do not change them.
Whatever is the last plugin to modify the material LOD object shaders is responsible for how snow LOD or ash LOD looks.
Below is the list of form IDs of 4 shaders used for object LOD:
- Skyrim.esm  SnowLODMaterial used for objSnow
- Skyrim.esm [0006AE38] SnowLODMaterialHD used for objSnowHD
- Dawnguard.esm  AshLODMaterialMtns1P used for objAsh
- Dawnguard.esm [04024FE0] AshMaterialSolstheimMtns1P used for objAshHD
The objSnow, objSnowHD, objAsh and objAshHD are identifiers used in the object LOD *.BTO meshes to map to the form IDs above.
Object LOD models for base records using a shader with "snow" or "ash" in the Editor ID are automatically part of objSnow or objAsh.
HD is typically applied to object LOD models which are using full textures, like for example the LOD for the nearest mountains which is using ..\Textures\Landscape\Mountains\MountainSlab02.dds.
Ash LOD shaders are used in the Solstheim worldspace.
The HD shaders make use of the vertex color alpha value. It controls the intensity. A value of 0.0 is low while 1.0 is high. The vanilla game uses ~0.4 for light snow (object LOD meshes ending in *l.NIF) and ~0.5 for heavy snow (object LOD meshes ending in *h.NIF) .