Not true at all. Here's a rundown of what's in Black:
- New remixed single player mode with different enemies/more enemies/harder (some from Hurricane Pack 1 on LIVE, most are new and now available completely offline)
- New non-essential plot cinema scenes including cool Ayane ones (not available from LIVE)
- The controllable camera in single player mode offline (not availabe from LIVE)
- New difficulty modes and rankings for Master Ninja Tournament (not available from LIVE)
- Over 50 new bonus missions (some from Hurricane Pack 2 on LIVE, many are new)
So yeah, it's pretty much brand new content most of which aren't in the two Hurricane Packs available.