The fact that the speed of light (relative to the observer/receiver)
varies with the speed of the observer/receiver is indispensable for
deriving the gravitational redshift so Einsteinians are forced to use
it, implicitly of course. The boldest among them believe that the
camouflage ("protective belt" in Imre Lakatos' terminology) is so
perfect that an explicit hint would do no harm:

http://student.fizika.org/~jsisko/Kn...Morin/CH13.PDF
David Morin p. 3: "However, the light takes a finite time to reach the
receiver, and by then the receiver will be moving. We therefore cannot
ignore the motion of the rocket when dealing with the receiver. The
time it takes the light to reach the receiver is h/c, at which point
the receiver has a speed of v=g(h/c).(...) The receiver and this next
pulse then travel toward each other at relative speed c+v..."

http://bertie.ccsu.edu/naturesci/PhilSci/Lakatos.html
"Lakatos distinguished between two parts of a scientific theory: its
"hard core" which contains its basic assumptions (or axioms, when set
out formally and explicitly), and its "protective belt", a surrounding
defensive set of "ad hoc" (produced for the occasion) hypotheses.
(...) In Lakatos' model, we have to explicitly take into account the
"ad hoc hypotheses" which serve as the protective belt. The protective
belt serves to deflect "refuting" propositions from the core
assumptions..."

Pentcho Valev