DIA can be a bit slow compared to UKY. But it's certainly worth having a look at. However, to try to answer your question... he's going to need help if your plan is to set up shop immediately. It will take time for him to build credit so either he will need to rely on your credit history, if you still have any, or on friends or family who are willing to help.
Renting a place to have the tattoo shop in is probably not that hard. I know many expats who have done residential rentals without credit. But if he needs insurance and equipment, that might be the stumbling block. Given the specialzed nature of his work, you may end up having to research this very specifically (i.e. phoning insurers, suppliers, etc) to see what they say.