Ultimately it's not possible to determine whether a pixel entry was made with only a pencil tool because everything can be faked and there's never any solid evidence that someone used it exclusively. If we wanna be really strict about it then you'd get next to no participation in these battles.
It doesn't even matter what the style is. I could automate the entire thing and then fool all of you guys while I run away with all the medals. I'd do this just to spite everyone who sees this strictly but I have more fun things to waste my time on.
Let's not make BotB a NO FUN ALLOWED place tbh.