Nechoma, if you keep the entire sefira except Lag BaOmer then I think the night is mutter. It’s only those who keep only 33 days that have a problem because Lag BaOmer is one of the 33 days so you need to keep miktzas hayom.
Those who celebrate a hilula rashbi have a heter of music and dancing since it is a mitzvah (sort of like those who matir music on Yom Haatzmaus) but to stam listen to music by yourself not as part of the hilula would be problematic. The same concept goes for someone who goes to a wedding before Rosh chodesh while they are keeping sefira, you can dance at the wedding but shouldn’t listen to music in the car on the way back.