Yes, but those are usually for NON-fiction.
New fictions rarely have them. LOTR and others by
established authors are the
exception. Remember that LOTR was first published in the mid 50s, so the device is dated and can be seen as pretentious.
Your editor will decide whether or not one is even necessary for the book--especially a debut novel.
I would suggest leave it out for the submission process, then have it in when an editor or agent requests a full and let them know about it.
I would suggest a talk with the co-author. He or she may have worked hard to assemble a lot of background info and want the validation of inclusion--but is leaving it in worth losing the opportunity of making a sale?
However important the info is to the co-author, your editor may see otherwise.
Besides--if the book sells you guys can put the appendix up on your WEBSITE!!!
An appendix can be seen as pages of infodump, which is the death knell for an otherwise good story.
You'll find this in the
Turkey City Lexicon under: "I've suffered for my art (and now it's your turn)."
It's a wise magician who keeps the secret of the illusion. The magic goes away when you explain it.
And above all,
LESS IS MORE.