I am installing Win 7 Retail Ultimate from the 'Windows 7 installation' and plan on using Daz loader, but I am not sure if I need a product key for this method?
Any loaders will integrate a Key for you. They also install a cert that makes Microsoft think your PC is a store-bought one So to answer your question: No. Leave the key space blank when installing.
Using loaders? Depends on, legal in the matter if you have SLIC 2.1 in BIOS as WL will only install key+cert Illegal to circumvent activation if you dont have slic 2.1.. The loader itself isnt illegal, but its illegal to use it.