Hi Martin,
The problem with setups in which the real servers are not directly connected to the ACE is that, it's not trivial to ensure that the return traffic from the serves towards the clients goes back through the ACE. Source-nat is one of the ways to achieve this, and probably the easiest one, but there are other alternatives.
It is also possible to route the traffic until one hop away from the ACE and then apply policy-based-routing to send this return traffic to the ACE
Regards
Daniel