Ecocomplete is porous, and to some extent will retain whatever fertilizer it can sequester, but there really is no appreciable amount of useable nutrients in the fired clay. The minerals in it are bound up in a crystalline structure that isn't useable by the plants.
Flourite makes the same claim about having nutrients, but although the elements listed may be there, it's somewhat misleading to refer to them as nutrients. The glass your aquarium is made from contains iron, but nobody is claiming that aquarium glass is a nutrient source.
I suppose that lithotrophic bacteria could eventually break fired clay down into a bioavailable form, but for all practical purposes, ecocomplete is inert.