Mark, I tried running rexx.exe directly against a rexx program but it failed in the same way. Actually ooDialog.exe is not used by the app so it shouldn't have been on the list in the first place.
Long time ago I tried to compile ooRexx on my own but got so many problems that I gave up. And I haven't tried since. But maybe it's time for a new attempt. I will have a go but may need guidelines on the way as I've understood it's a different beast than the rest.