Gareth,
You will probably have better luck asking Ninja questions on Martial Talk, as they have people involved in various groups that actually post there. The Ninja portions of e-budo have been virtually ignored since the original owner, John Lindsay, moved on into the mercenary world.
There are legitimate and hard-working groups that have involvment in the "ninja" arts, but there are far more whackos and egotistical nutjobs than there are legitimate practitioners. This is due, in large part, to how Masaaki Hatsumi chose to build the Bujinkan membership.
Here's my take on it, but it's strictly my personal opinions ... Dean Eichler is a ninja obsessed personage with no academic standing as a historian. His opinions are only opinions, and how historically accurate they may be is entirely up in the air. Christa Jacobson has solid ties to both Count Dante and Ashida Kim. That makes her quite a bit less than legitimate, as they were both seriously deluded characters from the 80's ninja boom.
Paul Smith
"Always keep the sharp side and the pointy end between you and your opponent"