Incase anyone runs accross the same question. After an hour or 2 trawling through the EAL4 config guide again I came accross this. So Yes, it is required.
Inspect ARP
To configure the ARP inspection engine, use the arp-inspection command in global configuration mode. ARP inspection is required when a firewall context is operating in transparent mode, to prevent IP spoofing of traffic.
To complete the configuration of ARP inspection the administrator must create static ARP entries for each host protected by the firewall context.
hostname(config)# arp inside 1.2.3.4 0050.abcd.1234
hostname(config)# arp-inspection outside enable
hostname(config)# arp-inspection inside enable
Cheers Chris