Be sure you have your facts straight, then discuss the laws and governance in a polite and discrete manner with these guys (without disclosing any names, YET)
South Dakota Department of Public Safety
(http://www.state.sd.us/hwysafety/ - broken link)
South Dakota Department of Public Safety: Enforcement: Highway Patrol
Then validate any LEGAL infractions or potential cause for concerns (realizing that emergency vehicles and operators are exempt from many DOT and ICC regs).
Find a third party to mitigate your concerns w/ management (it MAY be counter productive to have the LAW shut them down, better for all to 'mitigate' concerns and improve safety w/o the 'witch hunt'.) The owner will realize he is jeopardizing his profitable business, it is far cheaper for him to manage this than to face a lawsuit. EMT/paramedics are very cheap for the care they provide. Having relief personnel is not a problem for owner. There are a lot of highly skilled paramedics on their way home from Iraq, they need JOBS.