Mel Fisher was going after an actual historical documented treasure.
The oak island scam has been going on for over 200 years with each new promoter claiming a different kind of treasure, fake finds, etc.
Doesn't change the fact that there were people that called him a fraud. People that don't really know can say all kinds of things.
As far as Oak Island goes, nobody really knows exactly what is buried there, so there's a lot of different theories or ideas as to what may be buried there. There is documentation, it wasn't just that article in Reader's Digest, which I read as a kid. Ship Captains from that time wrote about Oak Island in their journals, there are carvings and symbols on rocks and markers, not just at Oak Island, but also in France and Portugal. The rocks & markers with symbols on Oak Island line up perfectly and are constructed the same way and using the same symbols that the Knights Templar used.
They've found roman coins, along with coins from other parts of the word on Oak Island. Artifacts they've found have been carbon dated to medieval times. Lead that they've found has been tested and determined that it comes from a specific area in France. Each of these may not appear on the surface to be the answer to the mystery, but combined, they all add up to paint a picture that something happened on Oak Island a long time ago.
They may find the treasure, they may not, but somebody hundreds of years ago went through incredible trouble to design such an elaborate and complicated system for hiding whatever it was that they were hiding. Personally, I feel that if it was just a chest or two of gold or other "typical" treasure, they could have probably gotten away with digging a 40 ft hole, cover it up, and nobody would know it was there, except for the depositors. It wasn't like Oak Island was a tourist destination in the 1700's, so probably not a lot of people visited that island, except for the large number of crew who lived on Oak Island for who knows how long, to dig tunnels and holes well over 100 feet deep, and to have designed water traps to make sure whatever it was that they were hiding, stayed hid.
To me, there's just too many coincidences and too much work that went into constructing the elaborate hiding place of whatever they buried. That's a tremendous amount of work to hide a chest or two. It had to be something of incredible historical value and significance. I guess we'll have to wait and see how it plays out.