Multiple F5 DNS as primary DNS server

Having a redundant zone master in BIND is possible but uncommon, administratively exhausting, and with little fruit. I suggest you just make your master the DC f5 and call it a day as there is not much to be gained from a redundant zone master. The slave will continue to serve requests even if the slave reboots as zone info is not just stored in memory on the slave but rather in files loaded upon boot. The only way the slave would stop serving requests is if the SOA expire timer runs it's course since it last communicated with the master. The default is one week on the f5 and can be increased. In the event that the master is down and you need to make changes on the lone slave, or if the master will be down indefinitely, you can easily change the zone config of the slave to be the new master. This would be the most downhill road.