Tommy,
I think Brett makes a valid point in that sleepers in the 60's and early 70's were strictly in the domain of the Dye's, and as such got "type cast" as a Dye feature.
In addition to Harbor Town, I believe a par 3 at Crooked Stick had some sleepers, but not in a bunker, but, my memory could be hazy on that one.
The angle of the sleepers is the critical safety issue.
Garden City Golf Club had sleepers in the bunkers.
I don't know when they were removed, but the pictures of those old bunkers sure are neat.
I seem to recall that Baltusrol Lower's 18th had a deep bunker with sleepers that was later removed. I believe Rick Wolfe could fill you in on that. (no pun intended).
When we ask why modern day architects don't copy special, classic holes, I think the same applies to sleepers. My view is that it would be deemed "unoriginal" and a "Dye" feature, and I doubt that only a few architects, those that worked for Pete, would venture to introduce them via their designs.