I think Gio, regardless of the validity of his arguments or any of his personal flaws, is well within his rights to present whatever evidence he has, for whatever reason he has, since Andrew Hussie is a public figure and the ethics of whatever partnerships they establish through Homestuck Inc./WhatPumpkin/whatever are a matter of public interest, especially as it involves fan creators.

Hussie/Homestuck as an entity aren't under any obligation to respond to this with any evidence of their own, and indeed may be unable to do so in some instances, but they have every motivation to offer some kind of counter evidence if they don't want to forfeit the entire narrative to Gio.