yes with ferts they might grow more. i have tanks with co2 and no ferts and never had a issue. i think telling people they have to add ferts or something will happen is wrong. i am not saying dont add ferts i am saying you dont have to but you could.
add ferts if not done right can bring up more issues then not adding them at all.
It also depends on your bioload. If you have a heavy fish load, and low to mod-light plants, you can check to see how things grow and what they seem to be lacking, but IMO using carbon without a Potassium source, will cause deficiency...it is science, I didn't make it up.
