PROXYSQL configuration over mysql galera replication
Yes, I would think so. In the ProxySQL blog post here there is a reference infrastructure which has multiple ProxySQL instances connected to the same set of database nodes. It also says:


  We usually recommend to setup ProxySQL instances on the application boxes for availability reasons 


That said, for a Galera cluster, I'm unsure whether the ProxySQL instances agree between themselves which Galera node is the "master" and which are the "slaves" - this is especially relevant if you're using read-write splitting, which is something you may want to do with a Galera cluster in order to avoid certain deadlocks not seen with ordinary MySQL configurations. (See also: Galera’s big gotcha for MySQL users.)