You do not need to cluster tomcats themselves for use with load balancer.
You can, but you don't have to.
Benefits are negligible. Session failover in tomcat cluster with BOE webapp is not fully functioning as in certain workflows will still show error to the user in cases of failover.
You should cluster tomcat if you're familiar with tomcat clustering and its troubleshooting.
You'll need test and verify it is working without BOE webapps first.
On your LB side you need to ensure proper session persistence is set.