It is possible to RNG abuse a perfect Pokemon. I have plenty of perfect 31 IV Shiny Pokes in my game, all legitimately RNG abused.Um... no, and I don't know why you would think that.
It's technically possible.
It's very, very, very, very unlikely, but there's absolutely no reason for it to be impossible (that I know of).
I really want to be corrected if I'm wrong here because that would uproot a lot of my feelings about the way hacked Pokemon and the game mechanics work. >_>"
I thought I should toss this in as a side thought to the scenarios I posted-
The Ditto could have been Rare Candied to level 100. But that would be to serve as the possible reason to just keep it from gaining any EV's to mess with the IV calculator for Breeding.
And, I can not find any other Pokemon that could be captured at level 100 besides that rare accurence in encountering the level 100 Magicarp in Platnium version of the games. (Unless that extends into Diamond/Pearl, but I do think the level 100 Magicarp thing is Platnium only.)