A load balancer can provide HA if have two or more load balancers for redundancy that provides one virtual IP address (or more) as endpoint for the clients.
If the LB node holding the virtual IP goes down, the virtual IP will failover to a still active working LB node.
I think it will work if you take two Pi's/nodes that can do both the LBing and be members of your load balanced DNS/HTTP farm.
I noticed latest Zevenet (former Zen) is also available for Stretch now:
I really have no need for this at the moment and am too busy with other projects to try it out.
But if HA is your thing, a load balancer can come in handy for redundancy and ease of maintenance as you can take down a node at any time.