Purpose of overlay for bow is protect tip from string when using a soft bow wood.
I think you want for decoration?
If so, it is not matter much density of wood, but more nock design. You want smooth curves and transitions to reduce stress points for string to dig/split. Same idea as fade in bow handle, if too sharp it will splinter. You can also thicken string in these area as it will add more cushion. Biggest problem on any type nock is bowyers knot, since it become tighter when bow is drawn, so, especially this area needs thicker string.
Cherry wood is fine I think, I would not even think of problem if I were to use, it is all about design. I think maybe under .50 sg I may worry a little.