I unfortunately do not agree with giving dogs any kind of commercial supplements that were intended for human consumption (except for a few like fish oil supplement, vitamin E, etc if necessary), and I also am weary about products designed for dogs as well, so I can't blame you there, I dont even feed my dogs commercial foods anymore.
If you are looking to supplement your dogs diet, add natural things into the meals. Like I said, Vemma seems to be heavily fruit and veggie based - all ingredients which are not beneficial to a dogs health. They are carnivores. Id also question some of the ingredients of which dogs shouldn't ingest period.
If you feel you need to add a little boost into your dogs' diets, try adding things like raw eggs, raw oily fish (like sardines, herring) - many many grocery stores here sell large frozen sardines in the frozen fish section, particularily Save On Foods. They're cheap.
If you're okay with raw, try adding a raw meal occasionally with bone (chicken/turkey necks, chicken backs, chicken quarters, etc, etc)
Also, some people also like to add probiotic, you can use low fat plain yogurt, or my preference is goats yogurt (my dogs get this for more as a treat than anything, not necessary in their diet)
Some people choose to add some fruits and vegetables to meals, I'm okay with that - however, its not really 'necessary', it won't kill a dog to eat some plant materials, but it certainly doesn't benefit them a whole lot (in my opinion). But if your dogs enjoy fruits and vegetables as a treat, add in green beans, carrots, or fruits like apples, pears, and some people like to give their dog the odd blueberries, but again, they won't benefit a whole lot healthwise from this, its a tasty filler more than anything.
You can also supplement the diet with green tripe, wether raw or canned... raw preferably. This is usually the only source of plant material I offer my dogs on a regular basis. Some people like Kelp, too.
There are many ways to supplement your dogs diet naturally, I would consider this before adding in something that was intended for humans, and not really beneficial for your dog. However, if you trust your vet ( I dont trust many at all - they are not well trained in dog nutrition) then talk to them about ways to supplement the diet naturally, if your not a fan of commercial supplements.
If you feel comfortable giving your dogs a commercial health supplement designed for humans then thats fine, they are your dogs. Its not something I would recommend, just because you take it, doesn't mean your dogs should. I cannot stress enough that dogs digestive systems are nothing like humans, and they have very different dietary needs. It worries me how many people apply human like traits to their dogs "Well this is good for me, so it must be good for my dog, too" - totally not true!..Just be careful, although you may notice some positive side affects, doesn't mean there couldnt be harmful long term ones caused by it, especially if given over an extended period of time.
I'm no expert as far as the mangosteen is concerned, nor am I personally experienced with feeding my dogs fruits rich in antioxidants and wether its necessary or not, but I do follow the belief that dogs are opportunistic carnivores, meaning they thrive on meat, and will get by on eating whatever they could find if they're starving to death. But generally, I dont believe dogs are designed to digest and thrive on plant materials, but this is just my personal belief..but some would argue that this is scientific fact.
I'm sorry I can't really provide the answers you are looking for, but I would still discourage you from offering these supplements to your dogs. The fruit might be fine, ensuring you aren't feeding the seeds, but I would just be cautious with the amount you give, and ensure otherwise that your dog is still eating a proper, nutritionally balanced diet.
