You aren't able to loot another person's kills, however if you see another person make the kill you can (as a chef/artisan) snipe their harvest, and I'm not sure if it's still in at the moment, do so before they actually have looted thus removing the enemy and it's drops from the field.
Perhaps a compromise is in order. Personally it doesn't bother me too much, so take with grain of salt and spoonful of sugar:
Allow the hiding gather, but slow the rate of the gather down. Movement is slowed during hide, so why not gather? A level 1 thief can still gather in high level areas, but not as fast as higher leveled character who is actively dispersing with enemies.