Ann: Exclusive Heads of Agreement Signed with Hyundai Engineering, page-33

I did comment above
It would not be surprising if HEC still sub contracts out parts of the project to local consulting groups as Australian mining expertise ranks up with the best in the world.
Certainly HATCH would have been one of the possible options on the list of the local consultants but as you have indicated above I expect past work done would put them towards the top of the list and so if you were looking to advance the timeline for an updated FEED then a good way to go. There will have been advances in a whole range of equipment and processes since 2015 so it could be expected to update any work done so long ago.
Down the track I would expect that HEC could bring a lot of expertise to a wide range of engineering solutions to the project. So for example sister company https://eng.hyundai-es.co.kr/ with solar power for the project.

Hyundai Engineering Corporation has been involved with building plants to process the polysilicon required for solar cells.
https://www.hec.co.kr/en/business/process/8502

Certainly the possible linkages across the whole Hyundai group might be very beneficial. (Perhaps we will see David driving around in an Ioniq5 in the future)

DYOR and enjoy.