Hey Michelle!
Welcome to the Disney Parks Mom Panel! Thank you for bringing us your question.
Disney International Salute to Baseball is a great event. You must be so excited your trip is right around the corner.
I am not sure if you are asking to have music playing on the field speakers or if you just want to have music playing while the boys are relaxing between games. I checked the planning pages for this event and didn't see any information prohibiting music between games. However, if the music is impeding any games currently taking place the officials reserve the right to ask you to stop the music.
If you are asking for 'Walk-Up' music, you would need to check with the on-site officials. Unfortunately, I would have to assume the answer would be no.
I hope this answered your question. If I misunderstood what you were asking, please come back and see me.
Wishing you a magical Disney sports vacation and a pixie-dusted day!
Sue N., IN