It depends on the level of certification the EMT holds. In a couple of states, an EMT-Basic can intubate, in others, the minimum level for intubation is EMT-Intermediate, while in most states, there is no EMT-Intermediate, and the minimum level for intubation is EMT-Paramedic. Also, was the EMT a paramedic student? If the EMT is a paramedic student under the watchful eye of a licensed paramedic, then it's probably OK.
Also, who told you that he wasn't certified? A lot of people aren't familiar with our scope of practice, and they assume that intubation is not a skill that we are allowed to perform. Even nurses and doctors are sometimes surprised to learn just how much we can do in the back of the ambulance!
If he really was operating outside his scope of practice, and he wasn't authorized to perform that intubation i.e. an EMT-Basic, then I'd contact the State Board of EMS, and notify them of that. Even though an EMT-Basic may know how to intubate, they don't always know when or why. If they haven't recieved specific training on intubation, then they shouldn't be performing the skill.