Why are you invoking ad hominem when the question is precisely whether a particular person (not the argument) is worth debating?

Dawkins' point is awfully simple: (1) I find this guy's positions are objectionable, and (2) this would look good on his CV, not on mine.

Thus, no reason to debate this particular person. It's a perfectly well-reasoned argument to refuse; we needn't bother speculating on Dawkins' internal mental assessment of his chances against Craig because the obvious stated reasons are enough.

(There are reasons to doubt your claim even beyond the normal peril when telling someone else that their own account of their mental state is wrong--including, for instance, the observation that Dawkins often comes across as profoundly arrogant, and to the extent that this reflects his actual internal assessment, it suggests that he might quite fancy his chances against Craig even if the assessment is in error.)

While I agree with you that Dawkins tends to come across as somewhat philosophically and theologically naive, this has little bearing on the reasoning to debate or not debate Craig. And your apparent charge of a logical fallacy is particularly perplexing given the question at hand.