College botany courses suggest otherwise as any good text will show. In fact they'll do fine without root feeding but they need high levels of column ferts and very high levels of iron to replicate their native waters.

They will grow even better with some root fertilization (stem plants have no use for it, their tiny roots just hold them in place)

They use so much iron I feed mine washers and steel wool. Not a joke. An Aponogeton will wrap its roots around one and digest it completely in about a decade. You son't need to do this though. You can use CSM FE+trace powder.

"...nothing unsafe about root tabs as long as..."

Why risk it? Why use something made for tomato plants to save a few bucks rather that using stuff made for aquarium plants.

Even the stupid gelatin capsules rot and will give you fungus poking out of the gravel. Gelatin? Really? Does Jello in an aquarium sound like a good idea to you?

Get the right dry ferts make a very thick paste, let it dry.