If the target of an Aura spell is an illegal target as that spell tries to resolve, it won't resolve, it won't enter the battlefield, and none of its enters-the-battlefield triggered abilities will trigger.

Runes can target and be attached to any permanent, even one that isn't currently a creature or an Equipment. You can cast a Rune choosing a Vehicle as the target, for example. The Rune's enters-the-battlefield ability will trigger, and you'll draw a card. The Rune won't do anything while the Vehicle isn't a creature, but if it becomes one later, the appropriate ability will start applying.