Every cluster is an HA cluster (crevat: a beowulf cluster, but that's a totally different ballpark), that's the most basic, and arugably the best reason to use one.
Load ballancing could happen in the cluster. The cluster server would control it and ferry requests to the approiprate node.
It is true that MySQL would need to be able to handle running in an active active configuration before this would work. There is some software that would allow it to do it. I found this which appears to use some trickery to do it.
Josh