Actually, if the servers don't all have the same content and the load balancing is done based on round robin it's possible that a request could be re-load balanced to servers that don't have the content. I think the only way to guarantee the request would be tried against all the servers until one is found that serves the content would be to explicitly check each server using [active_members -list].
Another option for improving this might be to use RAM caching. Assuming you didn't cache 404 responses, you could reduce the number of requests to the pool by answering the requests from cache on LTM.
Aaron