First I would like to start off by saying I am sorry to hear about your husband. I know how he is feeling and I know the stress you are dealing with because of this issue. It sounds like he is having a form of Simple partial seizures. Sometimes the seizure activity is deeper in brain and a normal EEG cannot pick up the activity.
You might want to look into EMU. A week long EEG done in the hospital that is also recorded on video. Caregiver222 is correct, he should not be driving until everything is under control. He will hate it but you too need to realize that it is for everyone's safety.
Essentialy, the diagnosis is made by the existence of siezures themselves and not an MRA, EEG or EKG.. Most hospitals don't begin drug treatment until the third episode. Clearly this means that driving is out of the question, at least for a year, and an appropriate medication is in order, usually dilantin. What is difficult to determine is the cause. He needs a so-called "flicker" test, among others. After being on medication, and after an appropriate period of time, driving priviliges are usually restored. I would seek further evaluation from a facility specializing in epileptic treatment.