I had a CAT C 749S, Kev ( Skids ) came with me when I bought it. Nothing at all wrong with it, was an exelent bike. But the only minor hasstle I did have was with insurance. Its best to disclose its a CAT upfront and they then get you to send in inspection reports that its fit for the road etc. I had Snells Ducati check the bike over and write a letter on headed paper that the frame / forks etc were straight and road worthy.
If you do a check on it, it will always state on any check thats it was a CAT D forever now. So as Mr C says dont expect to sell it at a profit or same prices as other 748's.
The only problem I can think of ( and someone with the know will confirm this ) is if the bike layed on its side after the crash with the engine running and it was starved of oil. I dont know how you can check for this ?