From FreeSWITCH Wiki
There was an article recently about deploying Asterisk behind UltraMonkey. FreeSWITCH will probably work in the same manner behind UM so that's worth checking. Also note that you won't be able to do HA based on just DNS SRV and several servers if you have users behind NAT because the ports opened in the user's router will only be open for the server it initially registered to, which is why you need UCARP or UM in front to appear as one IP.
Also, The Db setup in this article is a single point of failure, so oyur mysql servers ned to be in a failover setup with heartbeat.