I've used High Availability (Active-Passive) with DHCP on ESXi UTM's since I could remember (7, 8 and 9). In this particular Copernicus release, it simply doesn't allow an admin that option.
I understand the concerns, however, instead of preventing it from being an option, I feel as though admin's should be allowed to make that decision for themselves; a warning instead of an error.
Cheers,
Kyle