I don't ever remember trying to piggy-back on another Puppy version. If the underlying Puppy distro is a full partition install, then it would probably work.In view of the fast-changing pace of Puppy, could your underdog script be used to incorporate an older Puppy into your current one?
Underdog itself never worked perfectly. The ability to run an executable will depend, as always on the correct dependencies being available at run-time. The chances of any one specific executable being runnable increase if the underlying system is library-compatible with the Puppy version used as the main launcher. The efficacy of Underdog could well improve/change this time round, since Barry is reviewing the implementation.
@Lobster :
The script you refer to is not rocket science at all. All that script does, is to remove or create an underdog.lnx text file with the aid of a command-line menu. This has the effect of enabling/disabling Underdog as the user desires.
Exactly the same thing can be achieved by manually creating or deleting the text file. I certainly didn't implement the Underdog feature itself - it was Barry who did that.
Other interesting things to research as regards connecting up distro functionality are debootstrap and the chroot command.