If you follow the prey model ratios of 80% meat, 10% organs (5% liver and 5% other secreting organ such as kidney), and 10% bone. And you vary the proteins and try to keep the diet red meat heavy.... such as beef, pork, venison, lamb, etc. Then you don't need supplements.
Exception... if the meat you buy is from the grocery store and not organically raised (grass fed beef for example), then you should supplement with omega 3 fatty acids. These are present in animals that haven't been fed an artificial diet of pellets and chemicals, which most feed lot animals are. That's why I LOVE to get wild game... venison especially, as it is the cleanest meat you can get.
I get most of my meat at the grocery store. So I supplement with oils. I rotate with fish oil, krill oil, salmon oil. I also like to do emu oil and coconut oil. I usually just do a different oil every day. Rotate through them. I use all human products for these. I personally feel that the quality control on oils for people is tighter than pet products. So I buy coconut oil, for example, that I use for myself and Brody gets it too.
Yes, I have fed cooked foods with raw. For example, Brody was getting venison heart for dinner. Well we were having grilled chicken. I cut off a few bites of grilled chicken and mixed it with his venison heart. No problems at all.
There is one vitamin/mineral supplement that I do like and use occasionally. Nupro. (not to be confused with nutro the food). It is a powder you can sprinkle over food or you can add warm water and make a gravy. It is the only pet product vitamin product that I would recommend.
"Having heard all of this, you may choose to look the other way.....
but you can never say again that you did not know." William Wilberforce 1759-1833