IP pools are purposely not replicated automatically, no way around it. This is to avoid the situation where users authenticating to two different ACS servers get allocated the same IP address.
Basically there's nothing in ACS where the primary and backups talk to each other about what IP addresses they've allocated (this woul be huge task and require some new sort of communication mechanism between servers). If the same IP pool is configured on all 3 servers, they'll just blindly allocate the next available IP address to users, and you'll run into scenario's where two (or more) users get given the same address.
The pool is therefore purposely not replicated, which means you have to go in manually and configure it, making sure you configure a UNIQUE pool across the 3 servers. This only has to be done once and is then there forever.
