You have 2 options:
1. Weblogic plugin which is used with a web server like apache or OHS
2. Use a hardware load balancer
You can see more details here:
It is not manadatory, and it is possible to load balance apps on different servers with the ProxyServlet. It's only that this will be running on a server from where the others need to be accesable.
Also, it depends on what you are using this environment for. The ProxyServlet is a good solution if you want to replicate an Enterprise environment and test the load balancing with a WebLogic cluster. However, if you want to run Production applications in this environment, then consider the above suggestions: either a WebServer or a dedicated external Load Balancer.