Yes, intelligent design is a valid scientific theory, just as evolution is. Science really knows little about evolution and intelligent design, and neither has been proven or proven incorrect definitively. There also may be ways that the two theories coincide or are not inconsistent. Because this is an unsolved issue, intelligent design is a way of explaining scientific observations, and as such, it is a valid theory.
Intelligent design has no evidence to support it. It can't predict anything nor can anything disprove it because it is so vague since it simply says that life is to complex to have happened by chance so something must have created it. It's obviously just a new term for creationism after they found out that adding science to creation doesn't actually make it science. Being a new term for creationism is evident from the fact that their are only 2 possible creators: some alien from 3.5 billion years ago or God. If it were aliens they would have to continually come back to Earth to implant DNA to guide evolution; so the alien creator is unlikely. So what they are most likely talking about as the creator is God; in which case it's creationism. There's also one problem with it that makes it not possible to be a theory; vestigial structures. A vestigial structure is a biological structure that has no purpose or is not useful anymore. An example is the molar tooth, It has no real use anymore and almost always needs to be removed. If there was an intelligent designer they weren't to smart because those vestigial structures and behaviors in many animals show poor design. Why would such an intelligent being design humans with useless wisdom teeth that need to be removed? Intelligent design cannot explain these vestigial structures but evolution can; if intelligent design is correct animals should have much better designs; because they exhibit poor design a lot intelligent design isn't consistent with all the evidence. Since it's not consistent with all the evidence nor can be changed to fit the evidence it is not a valid scientific theory. Intelligent design is religion.
As long as the ID proposition cannot exclude the possibility that the designer is an omnipotent deity it is unfalsifiable as such a deity could, by definition, create any possible evidence. A model that can be stretched to accommodate any possible evidence and any possible outcome of an experiment is obviously useless from a scientific point of view. It explains nothing, no predictions can be made and no new knowledge can be gained from it - a complete dead end.