Do I have to tell them I am on the dining plan?
If it's not required to disclose it then it's not important to server how I pay.
I like the idea of saying we may pay OOP on this meal.
If I get good service I will tip even if it is included. Bad service has no re-course they get the same amount. I would prefer to leave them guessing
It's very considerate of you to treat your server with so much respect.
No, you don't
have to tell the Host/ess (who will ask) that you're using the
DDP, and you don't
have to tell your server. You also don't have to tell either one when they ask if anybody in your party has any food allergies (which one or the other or both likely will, as well).
They ask these questions to make the process easier for the GUEST. If you do tell your server you're paying with the DDP, she or he will be able to tell you what, if anything, is not covered by your credits - such as 'fancy' drinks in some places, or separately-priced side dishes.
If you choose not to tell them you're using the DDP, or to tell them you have the DDP but have not decided whether to pay for your meal with those credits or with cash, you potentially cause problems at the very least when it's time for the check. If you don't tell them, then order items not covered, they will bring you a check with everything. When you then present your KttW and say you want to use table service credits, your order will need to be rerung on two separate slips.
Please note: When you use DDP credits AND order items not covered, you WILL be charged an automatic 18% gratuity on the items for which you pay cash.
At any rate, do whatever you want, but reringing the order will delay your departure and possibly cause you to complain about the poor service at the end of the meal when you were trying to get the check and rush out of the restaurant to see Wishes/Spectro/Fantasmic!/etc.