It really depends on what "0" means.
Most test kits would register undetectable nitrates because they do not have resolutions low enough to show the actual values (which may not be really 0).
The 0.25ppm-1ppm recommended nitrates value is to ensure that all zooxanthellae get their allotment of nitrates, without overfeeding them and causing an overpopulation. As well as ensuring that nuisance algae do not have sufficient food source to thrive.
"0 Nitrates" is really two topics in one.
#1: Zero nitrates lead to other algae/bacterial problems.
To a certain degree, this is true.
Several strains of algae and bacteria take in nitrates in combination with phosphates and other waste material as their food source. So their presence reduce nitrates and phosphates at certain proportions.
Rapidly removing nitrates will mess up this equation and starve out these strains. This then opens the way for algae and bacterial strains that do not use nitrates. So you are switching from one nuisance to another.
This is related to how improper management of carbon dosing eliminates green hair algae, but leads to cyanobacteria blooms at the early stages.
#2: Zero nitrates can starve corals.
This is plausible to a certain degree.
Corals do not feed directly from light. It is the zooxanthellae that require it to make their food.
Zooxanthellae require more than just light. They also require minute amounts of nitrates and phosphates, among other things, to synthesize their food.
Their waste products are then essentially what provides majority of the coral's food.
In an aquarium that is heavily stocked with corals, having ultra low levels of nitrates could mean that zooxanthellae are not getting sufficient nitrates and could lead to corals starving.
