XML is great for scripts other than HA; make sure that the share is available for all account contexts on all hosts, and you're good to go. Performance is not a problem - the configuration is only checked / used at a certain time, for example, when starting or adding / removing a host. The SQL Server configuration is indeed aimed at higher availability (although in itself it is prone to service failure when SQL Server becomes unavailable as much as possible.)
By the way, the disk file will almost always be faster than access to the database for this kind of work.