Will moral philosophers behave better than non-philosophers? Kant seems to imply as much. From the Groundwork (1785/2002, Ch. 1):
A wonderful thing about innocence -- but also something very bad -- is that it cannot defend itself very well and is easily led astray. For this reason even wisdom -- which otherwise is more a matter of acting than knowing -- also needs science [i.e., Wissenschaft: academic learning], not in order to learn from it, but in order to gain access and durability for what it prescribes. Human beings feel within themselves a powerful counterweight opposed to all the commandments of duty... the counterweight of needs and inclinations.... From this there arises a natural dialectic -- that is, a tendency to quibble with these strict laws of duty, to cast doubt on their validity or at least on their purity and strictness, and, if possible, to make them conform better to our wishes and inclinations....Generally speaking, Kant interpretation is not for the faint-hearted, but this passage seems straightforward enough, even lucid: Without philosophy, our moral thinking is apt to be tangled up with self-serving impulses. We're apt to be led astray, illegitimately justifying just what it is that we desire. Philosophical reason, because it sees more accurately the true principles of morality, tends to counter such self-serving rationalizations.
In this way, common human reason is driven... to take a step into the field of practical philosophy. There it seeks instruction and precise direction as to the source of its own principle and about the correct function of this principle in contrast with maxims based on need and inclination. It ventures into philosophy so as to escape from the perplexity caused by conflicting claims and so as to avoid the risk of losing all genuine moral principles through the obscurity into which it easily falls.
From this it seems to follow that the more we beef up the philosophical end of the "dialectic" -- that is, the more we reflect on moral principles -- the more steadily we will see the moral right and the less will selfish desires entangle our understanding. This is the "science" that ordinary wisdom needs to "gain access and durability for what it prescribes".
As I see it, the issue is empirical. Does training in philosophical ethics help insulate one from ethical confusion due to self-serving impulses? Do ethicists engage in less rationalization? Does some principle, some unblinking knowledge of the right shine through?
Or, instead, does ethics tend to give one additional resources for rationalization? The ethicist may see more easily than others through the crudest, stupidest rationalizations -- but might this gain may be offset, or even more than offset, by a talent for subtle, sophisticated rationalizations...?