But I think one can share the RAW file they get that will correspond to UniWB, right? I think one can set in the camera to choose the reference RAW file to set the WB. I think there's a lot of share of these RAW files from Canon and Nikon. But seems no Olympus (or Panasonic).
No. The only way to set UniWB on Olympus camera is to shoot purple target, and you need exact target color.