There are many conflicting views on the matter, but there are loads of people out there with nice plants that didn't use "plant" substrates. Root tabs work, as does putting osmocote or minerilized soil under the substrate. Many people have successfully grown swords and other plants touted as being "heavy root feeders" with water column dosing alone. There's no doubt that substrate fertilizers are a good thing however.
My advice would be to use root tabs if you're going with an inert substrate, and dose the water column also.