This BZ has been around since RHEL 5 and most of it was addressed a long time ago. I will get input from the gss team at this point to see if this is still a concern to document.
Ah, at long last I'm looking at the BZ and can see that it isn't the big deal I thought it was years ago when I first looked at this. I think I can address this simply by noting how you can tell whether a dm table entry is open (and whether you can create a partition on it) -- noting when another program might have automatically created the partition already.
To get this off of the queue I'm moving this to RHEL 7 and should be able to finally address the issue with some embarrassment that it took this long. Once I get it in RHEL 7 and have it reviewed I can backport it to the RHEL 6 manual, but for now it will be RHEL 7.
Closing because I'm moving this to RHEL 7.
*** This bug has been marked as a duplicate of bug 1416898 ***