Yes, they are definately on that totally unreal pack. But you need to listen carefully here:
Atari screwed up when manufacturing the pack, they put the wrong stickers on the wrong cds.
As a result the actual bonus cd is labeled "return to na pali" or something. I can't remember what disc it actually was, so just run through all the cds until you find the REAL bonus content cd. It is DEFINATELY in there somewhere.
Remember though that the rocket arena mod only includes 90% of the exclusive dreamcast stuff because it is a deathmatch gametype. It only includes dom maps and dm maps ported to RA. You'll need to search elsewhere for the ctf maps.
I might finish sepulchure at some point, i've got more time now then ever before, but i really can't be assed to do laps in my house between computer and TV. Maybe i could just go from memory, it's a simple map. After that i can post it up here for you guys and any edits you feel are necessary to get it the way it was before can be carried out.
EDIT: I can see you're confused by the naming system. I know a way to clear this up for you quite fast. Just play the mod for 20 minutes. It should explain everything.
The RA maps are essentially 5 dreamcast maps stuck together in a single map. The only thing you need to do to separate them is draw a big box around the the arena of choice in Ued and ctrl-V ctrl-C them to a different .unr file.
Back to names: The arenas all are labeled by their correct, dreamcast names INGAME, so if you want to know exactly which arena it is that you are currently working on just play the rocket arena mod and find that arena in the game. Once you are there you should know exactly what dreamcast arena you are working on.