I've never watched his videos or trained under him, so my knowledge is limited, but... he came out with the DVDs in the mid-90s, when hardly anyone knew anything about submissions besides the Gracies (and a few other Brazillians), Gene Lebell and a few Japanese catch/Russian sambo guys. From what I understand, he had some good material, and even BJJ students learned a few things. So I wouldn't call him a scam artist. To me, a scammer either (1) teaches something of no value or (2) copies other people's materials. I don't think he copied others, because there was hardly anything to copy besides Gracie videos back then...and his style/teachings are very different (BJJ vs. catch).
Shonie Carter trained under him and had good things to say. Also, Mark Tripp and some other respected JJ/judo guys from the 1990s complimented him. Now whether he's modernized his teachings or whether they'd be helpful in 2017....I'm not sure. MMA and submission grappling have evolved a lot over the last 20 years.
There's also been some controversy about whether he really learned catch from Gotch or some other legend. To me, that's not really material--he somehow learned and taught catch before Josh Barnett...around the same time Frank Shamrock and Sakuraba were using it in NHB. He obviously learned it somewhere.