You could use a self signed cert generated on LTM or any other host in the client SSL profile. But the clients must have the root or server cert installed in their trusted certificate authority store or they'll get an untrusted cert warning.
You just need one SSL cert for all servers participating in the pool. This is the best part about centralizing your SSL certs onto the F5. It is easier to manage, reduces cost and it also offers a more robust environment.