Routing of DMZ F5 traffic to internal F5 traffic

I wouldn't consider it best practice, but people have their own opinions. Ask yourself this, would you open a rule up from the Internet direct to an internal server? If not, what protection do you think the F5 is adding to this connection to make your scenario better? Assuming you are just talking about LTM, it is working as a proxy and terminating the connection, but for the most part it will pass all application traffic, including application attacks/exploits, right through to your internal server.

As far as routing and firewall rules, that is configuration dependent, but I don't think you can just create a rule allowing DMZ F5 to talk to internal F5. Your traffic will go through the external F5 and have some source IP(defined by if SNAT is enabled, what snat pool you use, or automap) to a destination of the internal virtual server. I imagine you will need a separate rule for each VS you want to work this way.