From the sense of some of the spirituals, you are right, Greg. But the "rock" is applied in other senses. "I Got a Home in the Rock" seems to stem from psalms where God is called "the rock of my salvation." Another that seems to fit here is "Can't Hide, Sinner, You Can't Hide" with the verse:
I went to de rock, can't hide
Fer to hide my face, can't hide
Well the rock cried out, can't hide
No hidin' place, can't hide.

In "Move de Member" the singer says "Got on my rockin' shoes, Dan-u-el." Just an item of heavenly clothing since the spiritual goes on to mention the long white robe and the starry crown.
"Rock Mount Zion" from "Job, oh Job" seems obvious.
One sung at night meetings started with "Rocky, chillun, rocky, Jesus comin'" applies to a reeling and rocking dance.
Then there is the spiritual "Rock Er My Soul in de Bosom of Abraham" which ends each verse "O, de Rock Er My Soul" (Again, applies to God).
I seem to remember that the mound of Calveree is called a rock in one spiritual.

Just a few at random from the first book I happened to pick up.