Legal Question in Workers Comp in California

WC judges allow a very loose reading of the evidence code but I doubt any would allow such a letter in. It is not under penalty of perjury, probably only states that there is evidence of retaliation but does not draw a definitive conclusion, is not subject to cross-examination by the other side so they can refute it, probably does not detail the evidence presented, and has no binding effect upon the WCAB. You also then bring up the issue of which forum you are seeking redress, as normally you can not "sue" in two different bodies over the same facts and issues. You can use their report to try to gather other admissible evidence.

You should seriously consider if you want to go ahead without an attorney. 132(a) claims are hard to prove, claims based on retaliation even more difficult. People hire attorneys for a reason--attorneys often get better results.