I've spent a good amount of time this year doing research on the loops at the Grand Californian, so I can provide a little info.
As has been mentioned, Storyteller's does have its own music loop. There is also a hotel interior loop and an exterior loop, and the Napa Rose also has it's own music.
The music plays at a decent volume in the restaurant, however the speakers are located high, high up on the ceiling. Even when the restaurant is quiet identifying music using software such as Shazam has had very limited results.
I have never heard any music play at all in the restrooms, and I have checked specifically for it. Sea Castle, are you sure you're not thinking of the Napa Rose? It's also possible that music once played in there but no longer does.
The time that you dined at the restaurant is important- there are at least two different music loops that play. There is a main loop that is usually played at lunch and dinner, and there is also a special loop of Disney themes that plays during Character Breakfasts in the morning.
Items from the regular loop I have definitely heard include Blow the Man Down, a version that appears on a DLRP official album I have but may also appear on other albums, and music from the Cinderella soundtrack. I've also heard guitar tracks that sounded like the music that plays in the Golden State in DCA.
The difficulty of getting a clean recording, even a live one, makes IDing the loop a very difficult task. I have asked at guest services at the hotel in person for any and all information about the music that plays at the hotel and it's restaurants, and was sent to Guest Relations in the Esplanade, who in turn sent me to www.disneymusicloops.com (really). As far as I know guest services/relations at the resort does not have any loop information for any music in the resort. Obviously information about the loops must exist somewhere but finding out who has it and reaching them would be quite a project. I'm actually considering giving some of the loop information I've collected (such as the GC Exterior loop listing) to the hotel so that they'll have it if guests ask for it.