By following these steps, you will convert a model from 3dsmax with V-Ray materials, to SketchUp while keeping the exact same V-Ray materials.
Open file in 3dsmax.
Disable Gamma correction, as V-Ray for SketchUp handles it differently (otherwise you'll get very dark materials).
Export it as FBX.
Split meshes by materials using the script "Detach by Material ID" (click here to download it, then Scripting > Run Script) You need to do this to export materials as individual *.vrmat files, instead as one big file.
Go to "Tools > V-Ray vrmat converter", then "Convert Scene Materials to .vrmat" and choose the folder of the FBX file. This will create one sub-folder per material, with the same name as the materials.
Optionally, copy bitmap files to the same folder as the FBX file, to help Transmutr find them.
Load the FBX in Transmutr. It should automatically find all the .vrmat files exported earlier, and match them with the materials.
Transmute, open your file in SketchUp, open V-Ray so that it can convert the .vrmat data to actual V-Ray materials.