I've had it confirmed by TAC that you have to enable a DHCP server on the vlan, not just able to get it to act as a DHCP/BOOTP relay.
So we can;
a) Act as an ip helper / dhcp-relay and NOT a BOOTP forwarder, or
b) Act as a DHCP server (i.e. not a dhcp relay), and act as a BOOTP forwarder
Seems a bit contradictory;
a) Forward DHCP multicasts as unicasts, and DO NOT Forward BOOTP multicasts as unicasts; or
b) Forward BOOTP multicasts as unicasts, and DO NOT Forward DHCP multicasts as unicasts