Yes, plantsims and aliens can have baby together. The baby will have alien DNA (green skin, black eyes and hair if alien has it and alien facial features) and plantsim's human DNA (Skin and hair color before becoming a plantsim, eye color and facial features).
Life state isn't something that is passed on to babies. So two vampires will have a normal human baby. However, alien features do pass on only because aliens only have green skin, black eyes and alien facial features (aliens have no special powers).
