You're quite right that this can be an important distinction to make, but in this case it's moot. I read all the artists statements and all of them explicitly state both of those positions. Yes, they all directly supported Macklemore speaking out, but they all also followed that by stating some form of agreement with him on Palestine.
Finneas strait up says, "I stand with Palestine and its people". Aaron Rowe uses the phrase "Israeli genocide". Beoga says "We fully supported his message." and goes on to say a lot more about Palestine, colonialism and violence. The only one who doesn't specifically name anyone is Lukas Graham, but even he talks about speaking out against any violence on civilians and children, no matter who they are, which in the context of it being a response to Macklemore's statements should obviously be read to include Palestine.