Thanks for mentioning this, I soft reseted about 15 times early, and about 36 times just now.
( I used my Pokemon Sapphire version the first time, and a Pokemon Emerald version on an emulator the second time ) and not once has a wild pokemon appeared during the trained encounter.
While this also would screw up the game, it doesn't happen.
As a trainer, that hasn't ever happened to me, as a Gen III fan, it's also never happened to me.