Possibly, depending on how they're activated. If the layer is only activated while another key is pressed, that's not stateful (i.e. no different from yet another Fn key). I'd say that layer toggles and one-shot key modifiers are stateful control, yes.

Personally, I've found that I prefer layer shift keys over layer toggles. It takes more mental effort to track in which layer I'm working than to hold a key while pressing another. The only persistent layer toggles I use is to switch the entire keyset to a different layout (qwerty vs workman vs single-handed, or switch the right half to numpad).