If you are feeding a good balanced diet, research after research on animals AND people show we really don't need vitamin and mineral supplements. Really.
That said, adding in fish oil is fine and might be helpful.
I was surprised to see apple cider mentioned. Please do research before you add cider, vitamin C or anything that can actually change pH balance. Vitamin C I gave for 20 yrs until a dog turned up with some kidney calcification that UGa felt was potentially related to the Vit C or at least made worse by it. For me, the negative of supplementing Vit C AND anything changing pH level outweighs the positive, especially if kidney problems or iron retention are problems already. Changing pH levels may be related to formation of crystals and stones.
Lots here promote PlaqueOff, and based on it I bought 2 containers. Didn't see any benefits, then read THEIR OWN RESEARCH showing it helped for 5 weeks ONLY, then the plaque amt went up again. If their own research says not helpful after 5 wks, not worth my money. I doubt it will hurt anything.
On your veggies– fyi unless you pulverize them pretty much, dogs like them but get very little actual nutrition. I give the guys a lot for treats. :)
I believe in probiotics. But I used to also use a lot of other supplements. Now, I give supplements only if there is a problem (such as joint support/inflammation for which I swear by Bromelain!). Arwen, because she is on low dose steroids and has mild gum infections off and on and has to have antibiotics every couple of months-- I keep on SamE. When my vet suggested it I rolled my eyes. Research shows it does indeed help. I frankly take large amts of liveraid and believe it is why I am still alive, so don't think I am anti-supplements. I just believe if it really works, research supports it. (liveraid is primarily silymarion).