Hi,
HA and DRS are working separatly. So you just need to check if you want to prevent or not, that your VMs should be powered on if you loose a host. You need to check if your host have sufficient ressources to start your VMs. Because if you haven't enought ressource and admission control is enable, your VMs will not be restarted.
You can check here if you want more information regarding admission control : vSphere Documentation Center
Regards,
Julien.