Lag B’Omer is not a heter for listening to music during sfira, which is aveilus.
There is no aveilus of sfira during Lag B’Omer (with regards to music). However, an avel will still have their other aveilus, and as such, will not be able to listen to music.
To phrase it in Yeshivish, it is Hutra, not d’chooya.