(* Spoilers for And the Rock Cried Out No Hiding Place *)
Re: the rabbi singing the gospel song...a couple of points. First, if
you're visiting someone's church, it's only considered polite behavior to
go along with what's there. I have a number of Catholic friends who would
sometimes go to temple with Jewish friends...and when it came time to
sing, would do so. Why should it not work the other way around?
Second, as I seem to recall, the line about "no hiding place" is taken
from the Old Testament, which forms a substantial portion of Judaic
teachings (but not the whole of it, a mistake many make). Yes, there's
some later stuff worked in, but the heart of it is from a common ground.
jms