Last time I stayed at a MK resort was Wilderness Lodge, and I don't remember them playing any of the music inside--you had to be outside to hear it. Of course, you had to be outside to really see it, anyway, so that kinda makes sense.
I do recall that California Grille, which is a restaurant where you CAN see the Electric Water Pageant, does NOT pipe the music in. You can see it from the catwalk too, but unlike the MK fireworks music which is piped to there, the only way to get the sound is to be on the beaches/viewing areas (you can actually hear the music from the catwalk...it's not like it's total silence or anything...but it's a few seconds behind because of the speed of sound and bouncing and stuff).
I've had dinner at both 'Ohana (in 1995 & 1996) and the restaruant's prior incarnation, the Papeete Bay Verandah (in 1993), at the Polynesian Resort while the EWP was going by outside and the music was not piped in.
True, our responses don't give you an affirmation of your question, but they do help to narrow it down; in the case of my response, since 'Ohana IS, and the Papeete Bay Verandah WAS, a restaurant located along the Seven Seas Lagoon and it does NOT pipe in the EWP music through its speakers during the parade's performance. Of course I haven't been there in 6 years, so maybe someone else who's been there recently could confirm whether or not this is still the case.
So, to summarize, we know that three locations along the Seven Seas Lagoon and Bay Lake do not pipe the music in; all that's left are the restaurants at the Grand Floridian. Can anyone else shed some light on those spots?