I use vit c, as is recommended to help feet from turning out, and to help protect against Hod and Panno as i have Danes. And Omega 3,6,9. for hormone, joint and coat support..I also use a joint supplement for my older boy, which completely changed his life within a month, from a geriatric with arthritis to a dog who was able to keep up with his younger companion... And a good probiotic powder...Some supplements are very useful, and some a godsend. But nothing compensates for a good diet, in my dogs case i feed mostly raw..

Nah, i don't think so. A lot of what they need will be in their food providing it's a good brand.
The only supplement Millie has is Yumove for her joints as she started getting a little stiff at the start of the year. First supplements she's ever had, she's 11 1/2 and has only been to the vet with one illness (gastroenteritis) since we got her 10 1/2 years ago.

(tbh she was on Bakers until she was about 7 when i got bored and started researching dog nutrition and i'm very glad i did, she's on JWB now and has managed to obtain a wheat allergy )