The Zeovit system is honestly quite useful, but only under certain conditions.
Firstly, you need to understand that its mainly going to have a noticeable effect only assuming that the bioload on the system it is being set up on is heavy. Under a heavy bioload, regardless of what your filtration system is, generally there is a large benefit to having a strong and active bacterial colony, which is the whole premise of the Zeovit system.
As for nitrates and phosphates, yes and yes. In both situations, a Zeovit system would work. As mentioned above, the main concept of a Zeovit system is having a stable supply of bacteria in the stones kept inside the reactor with flowing water through it. Once in a while, this reactor is shaking, causing the bacteria saturated with nitrates and phosphates (their food which fuels their metabolism and subsequent growth) to be taken in by your skimmer. Speaking of which, A skimmer is a definite must for this system. Without a skimmer, this will create a problem more than it will solve one.
So in the end, I suppose it depends more on the bioload you have, what size tank you have, and if you feel you have a potential nitrate or phosphate problem or will have one down the line. And yes, as an answer to your last question, Zeovit systems are generally used on tanks with SPS simply because SPS thrive in low nutrient (oligotrophic) environments which Zeovit systems help achieve.