Allegedly no, but Palmer was in the business of hiring people to do stuff like write articles supporting the Shaver Mystery. The speculation around Palmer is mostly based around Palmer's pattern of behavior. palmer paid people to perpetuate hoaxes, Arnold just seems the next level in a progression.
I’ve always felt Arnold was unknowingly used to help cover up an environmental disaster caused by a clandestine program nearby. Palmer was probably contracted to help carry it out.
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https://archive.org/details/makingofspy00palm