Yeah... that's right. macroalgae does absorb nitrates as a food source.
Please define the term nutrients as intepreted by you. It will confuse a lot of newbies. Nutrients usually means a source of nourishment. Nitrates can be a found of nutrition to some corals but to others, it's a form of poison that affects its health.
One coral's nutrient is another coral's poison!
Frankly, if you have sufficient water circulation from your sump, refugium to your tank, a state of equilibrium will achieved in a very short time. Unless you are saying that corals can absorb something in its immediate vicinity so quickly that nothing reaches the algae in your refugium.
hmmmmm.... interesting theory!