Almost all base morphs (original single gene morphs) came from one or more wild caught animals that were put into captivity. Those morphs can then be selectively bred.
I think that cage aggression (with ball pythons at least) is a complete myth. The number one reason NOT to move a ball python to another enclosure for feeding is stress. BPs can be very finky eaters and moving them around near feeding time can exacerbate that.
Het refers to heterozygous, or only carrying one copy of a recessive gene. Het animals LOOK normal, but have the genetic potential to create interesting morphs.