If someone who is a heroin addict throws up everyday, sometimes more then once, is it more then likely the heroin? Or could it be something else?

Either. Vomiting is a common symptom of heroin withdrawal. Heroin is very short acting and highly addictive. Your body starts to need it and the more you use the more your body needs. Within a few hours most of the heroin leaves your body causing withdrawal symptoms like vomiting, diarrhea, muscle cramps, and "the shakes." vomiting can also be due to many other illnesses.
Vomiting. Heroin is an opioid drug. Morphine, codeine, hydrocodone, oxycodone, all opioid pain meds can also cause vomiting for susceptible persons. Many other causes for vomiting as well, and this person should be checked by a doctor.