Since many bacteria are often opportunistic, adding food for them (i.e. carbon dosing) is likely to have a much greater effect on bacterial production than just adding more bacteria. The reason we don't have more bacteria in our tanks is because they're limited by some factor and in many cases, that's likely organic carbon. If we add more organic carbon for them, they might take off, incorporate N and P into their biomass and when we skim the out, boom, lower nutrients. That's all dependent on if they are in fact limited by Organic carbon, which the results of carbon dosing suggest might be true in many cases.
We certainly have a large diversity of heterotrophic bacteria in our tanks from live rock and sand so we shouldn't really need to add more to beneficially increase that diversity. If you already have some of these key strains in your tank (which we all probably do), they have the potential to take off. There might be something to adding bacteria to a new reef tank but honestly, I wouldn't know.
All of this being said, I've seen the results of Vibrant on this forum and hey, it can work! There's some potential that it could be just calculated carbon dosing but if it works, it works.
All in all, there doesn't seem to be a reason to add more live bacteria for nutrient reduction if the ones you have are already too limited to grow so in most cases, carbon dosing is probably much more effective for nutrient reduction.
I don't know much about how it impacts water clarity though and it seems to work so if that's why you add bacteria and it works, keep it up!