Attacking the credibility of a doctor performing a C&P examination, particularly in develop to deny situations is a question of pure legal strategy - on a case by case basis. There's a huge difference in attacking the merits of a negative report as opposed to attacking the credibility/proficiency/qualifications of the medical examiner. For instance, if a veteran has a solid IMO, then the attack only on the opinion merits may be warranted. At any rate, under the equipoise/benefit of doubt doctrine, the veteran should prevail. If the examiner's qualifications are challenge, one may be exposing one's self to a develop to deny scenario by having the remedy of another C&P examination.
These are advanced matters of legal strategy, you should seriously consider consulting with an experienced VA disability lawyer even to see if you are being subject to "develop to deny."