I guess I don't really fully
understand why the pure resistive losses in the coax choke wouldn't
affect the efficiency of the monopole.

A simple way to think of it is: Ferrite beads over the outer of a coax has
no effect on the signals flowing 'normally'
up and down 'inside' it. The beads only effect signals that are flowing on
the outer (treating it like a piece of wire rather
than a coax transmission line). I know that this is not quite the full story
but it is a simple explanation of the situation
under discussion.

Jeff