A Pokemon that is RNG'd is just like any other pokemon in game.
For VGC's I've used a combination of EV's and IV check/Capture, and Fast Hatch (one 2 of my Pokemon) and they have all passed.
Nintendo don't release their method of Hack Checking as that allows the hackers to exploit it. So I have no idea, the best way is to be safe and use Pokemon you caught yourself or from someone respected/trusted as mentioned before.