On the contrary, given that he has indicated a professional interest within the rationalist community, he should shield his early steps -- and the invariable (pit)falls they will lead him to -- from his one unchangeable identity.

Lesswrong usernames do not tend to remain anonymous among the rationalist community even among those who make (some, but not extreme amounts) of effort to hide them. Personality and commonly expressed beliefs tend to make identity rather obvious. On the other hand pseudonymity is enough to shield you from a token google search by a mainstream employer associating you with any non mainstream beliefs expressed.

Do note that 'better-than-usual' option is hardly a ringing endorsement. It's more a failure to advise against in this case rather than particular advice for. My only serious advice is to abandon any name that makes him look like a 13 year old troll.

Also, "wedrifid" advising the use of real names?

I have 27,746 karma worth of learning from that mistake.