I'm not sure about the system in the US but in Australia the S70C should be able to be registed as the C model was for civil use and for sale to countries with problems getting military versions eg; China, Taiwan, Hong Kong, though the main problem would lie in the spare parts supply as with only about 30 or so C models build any part available are actually for UH60 /S70A so the problem of military parts on civil machines rears its head.
The problem of maintenance , yes the Blackhawk is a high maintenance aircraft but not through Sikorsky's doing , if It was operated and maintained along the lines of most civil Helos, the maintenance would be greatly reduced, I worked on Blackhawks for 5 years and have worked on Super Pumas for 7 years now and I know which is easier to maintain and it aint the Super Pussy!!
If you look in Europe the average Super Puma flys well over 1000 hrs per year while a military S Puma is lucky to do 500 if you carried out the maintenance on a civil macine like a military one it would be on the ground more than it flys , a military 500hrly i have seen with Swedish, French and German S Pumas has taken up to 6-8 weeks while a civil one will be lucky to be down for a week or the serviceing is broken into zones for progresive maintenance, the maintenance is not to a lesser standard than the military operators, but the military machines are over maintained and on differant maintenance systems ,I believe if the Firehawk was maintained in a staggered maintenance system like cvil machines and not based on the US army system the costing would be lower and servicability higher. I think the Firehawk is a great Helo but unfortunatly there are only military operators of the Blackhawk family in general and unlike the S Puma which has a large civil as well as military operating base there is not the experiance base to draw on for civil use