On this last, if Heinlein had any kind of "personnel" responsibilities
during his time in Philadelphia, there's little doubt that he could
have been familiar with the methods used to detect and select for
young men with the potential to absorb highly technical training.
The Navy in particular had been administering such tests for
decades, emphatically so in screening enlisted men for the
Submarine Service, which was probably THE most technically
demanding field (in terms of what was expected of even the
most junior enlisted men) in the armed forces.
If Heinlein were really trying to help his fellow SF writers avoid
the risks of front-line service during the war, one has to wonder
how well he knew Cyril M. Kornbluth (for example), who had
been a member of the Futurians and had certainly known
Asimov thereby. Kornbluth served as a machine gunner in
the European Theater of Operations, and was awarded a
Bronze Star for valorous service during the Ardennes Offensive
("the Battle of the Bulge"), so he was most definitely up
front where he could've gotten killed.
It might be expected that Heinlein's motives for drawing
de Camp (an aeronautical engineer) and Asimov (a
biochemist) into work for the Navy in Philadelphia were
borne more of the fact that he knew both men quite
well, and understood that the Navy could benefit from
their talents and training in that facility. Think "networking"
in the days before the 'Net.