No, they don't. An insider is someone with inside knowledge. Period. Someone who disagrees with the policies of a company but stays on is just as much an insider as someone who doesn't disagree and stays on.
That is a response to the argument (it might be valid, might not I'm bowing out of that debate). By making that counter argument (the importance and effect of the credibility) of the defining parameters of "insider" your conceding it isn't fallacious - because your countering the argument. Your better argument than ad hom would be the importance of the argument is minimal when compared to the substance of Palmer's cumulative case.
There ARE legitimate uses of ad hom, but that isn't what you've been saying - you've been saying it isn't an ad hom at all.
I'm saying it isn't fallacious and that amounts to the same thing. Legitimate Ad Hom is no fallacious so you use of deriding it as ad hom is fallacious. I am more concerned with legitimacy of your arguments not semantics. I am happy to concede whatever semantical compromise you want to make.
By the way, their criticism of his honesty/integrity are well off the mark too. Palmer was upfront with his supervisor about his feelings all the way through.
I don't know the man.
best, mikwut