Pardon them for what? Unless their possessing firearms wasn't in line with the law, or that "physical altercation" mentioned that questioning apparently went nowhere reemerges as a thing then I don't know what they'd need pardoned for based on the article.
The marching with Nazi shit and spewing whatever hateful bullshit is protected speech, because speech protections in the US are extremely broad.
And that's before getting into whether or not the hypothetical crime is federal (which he could hypothetically pardon) or state (which he can't).
They're marching in the hopes that someone will attack them in a fashion they cannot reasonably flee from? Or does Ohio have stand your ground and we could knock the part about fleeing off?