Either is fine. We don’t have a HaldCLUT folder for emulating camera effects, but neither do we have that for PP3 files, so we could make one. PP3s would be smaller. HaldCLUTs would be “cleaner” if you know what I mean.
Have you used the 12-level identity file, as described in RawPedia?
http://rawpedia.rawtherapee.com/Film_Simulation
Save it as an 8-bit PNG with maximum compression. Don’t worry about it being 8-bit, RT’s HaldCLUT algorithm interpolates the missing values and I found no difference between using an 8-bit vs 16-bit file, other than 8-bit being smaller and faster.
If I remember correctly, the ImageMagick command I wrote in RawPedia and the identify file I bundled in the zip handle the gamma issue, so your HaldCLUT should just work if you use either the command or the sample identity file.