Now that I don't need it, because I got everything running correctly and can boot RT-11 for RL02 disk, of course the first random RL02 disk I tested was XXDP+. This kids is how the world works.
Anyway, I loaded the XXDP+ program from RL02 drive 1. The program is not Y2K compatible, so I entered a date of 01-FEB-88
The XXDP+ monitor came up and gave me a dot prompt. Note that when you run a diagnostic, enter ?? at the end so it finds the version that happens to be on your disk, otherwise you'll get a lot of not found errors. For example
. R BKTG?? (run KT11-D Exerciser)