(I'm getting off topic here, mods feel free to split this off)
The insurance and liability issues would be expensive but easy to take care of with good coverage and an ironclad waiver, just like whitewater rafters and skydivers do hundreds of times a day.
The main obstacle I know of is what Steve Marshall pointed out before - the Federal regulations on commercial for-hire transportation, which for a chase tour are very prohibitive in cost and logistics (IE, getting a CDL, the 12-hour restriction on driving, rigorous vehicle inspections, etc). Apparently most tour companies either have been exempt from these somehow or are 'flying under the radar' so to speak. I'd be interested to hear how tour companies are dealing with this!
I would never go out and run a 15-passenger 'rollover of death' van operation, but two storm-hungry people riding in my back seats while I and a chase partner enjoy an all-expense paid chase vacation - are you kidding? I'd do that in a heartbeat. Apparently there is enough demand that the competition issue is moot.