Here is some information from the nick hotel website:
CHARACTER BREAKFAST
Enjoy a daily bountiful buffet breakfast in the Nicktoons Café! Guests of all ages will dine on a self-serve buffet while "hanging out" with some of their favorite Nickelodeon characters like SpongeBob SquarePants, Patrick, Dora the Explorer or the Fairly Odd Parents. The Character Breakfast will be available from 7AM - 11 AM and the cost is $16.00 per adult and $8.00 per child ages 12 and under plus tax and gratuity (the kid's eat free program is not valid on the Character Breakfast). Seating is limited so reservations are strongly suggested, call toll free 866-462-6425 for more information.
I called just a few days ago to inquire about the character breakfast for our September stay and they told me I couldn't make ressie's until 60 days out. So I have to call back in July. I don't know but I would guess that you don't need to stay at the hotel to eat there.