As far as I can tell, Bubba is his real surname, and 'Head', while
probably pseudonymous (it's often given in quotes), is preferred enough
that he's referred to as "Head" Bubba in Credit Suisse public documents.
I almost hope his name is pseudonymous: it'd be evidence that you don't
need to abandon pseudonyms even when you climb to senior positions :)
(One question remains unanswered: who is Shem Multinymous? Now there's a
name that just *screams* 'pseudonym'... :) )