Hello Gareth
Concerning the other types of OSPF packets, the answer is that many of these can actually be both unicast and multicast. It depends on the way in which they are used. Specifically:
DBDs are sent using the unicast address that has been obtained from the hello exchanges. This involves the creation and maintenance of a master/slave relationship between neighbours to regulate communication.
Whether or not multicast addresses (and which multicast addresses) are used also depends on the existence of a DR and BDR. Link State Update packets are sent to the AllSPFRouters (224.0.0.5) address while all other routers send both their LSUs and LSAcks to the multicast address AllDRouters (224.0.0.6).
An LSAck can be unicast when a device wants to acknowledge a received LSA to a single neighbour. However, multiple LSAcks can be grouped into a single LSAck to improve efficiency. This enables a single LSAck to indicate acknowledgements to several neighbours at once using multicast. So LSAcks can be both unicast or multicast.
In addition, retransmissions of Link State Update packets are ALWAYS sent directly to the neighbour. On multi-access networks, this means that retransmissions should be sent to the neighbour’s IP address.
Most of this information can be found in the OSPFv3 RFC.
So you see there is no clear cut answer, but depending on the situation, either unicast or multicast will be used on an Ethernet network. On non-broadcast networks, unicast is always used.
I hope this has been helpful!
Laz