The examiners of a friend's PhD thesis required revisions which they needed to approve before they would accept the thesis. The requirements were fairly demanding but overall reasonable and helpfully explained, and my friend wishes to acknowledge the examiners' contribution in the final submission, in anticipation of their approval.

However, it seems to me that examiners are not supposed to be friends; and any implication that they are seems to suggest that the examination process was too cosy, or that the examiners were perhaps rather a push-over or even somewhat corrupt. Are such concerns well founded, or am I worrying unduly?