They test to ensure the airbags will not cause severe injury to a person who is leaning against the side of the car (in the path of the airbag) rather than centered in the seating position. You're not supposed to lean in the path of the airbag and you'll be better protected if you're where you're supposed to be, but it shouldn't be super dangerous.
I'm kind of surprised they'd be able to move the 2nd row of a van much closer to the door. I'd think you'd have to move the 2nd row almost out the door before the passenger is truly underneath the air bag. A lot of other vehicles have seats that extend prettymuch all the way to the door and their side airbags still protect people rather than injuring.
Also, the side airbags we're talking about must be curtain airbags. Side impact airbags come from out of the vehicle seat itself, so moving the seat would move the airbag, too (or possibly disable it if it weren't wired properly). Side curtain airbags deploy with much less force.
I have to wonder if the guy your husband talked to knows what he's talking about. Is he truly qualified? Maybe they're not picking the correct vehicles for modification, either. I know a family that has had a van and a truck modified for W/C accessibility, a W/C lift, etc. They had a specific list of make, model and year combos that would work when they were looking for a truck.
http://www.nhtsa.gov/cars/rules/adaptive/brochure/brochure.html#Anchor-Investigate-47857