Also, I would be interested in the web site if you can find it.
And there are Haddemans that live in the Netherlands, one is Anton Haddeman, an avid stamp collector, particulary stamps related to radio. Edward Haddeman, a nutritionist and Edwin Haddeman, a nuclear physicist, another is Theo Haddeman, a photographer. I also just found a Sara Kirjka Haddeman, married to a Donkersloot in the Netherlands. I have also checked out the LDS website and it has some of the info you've already provided. It did mention a Harry Haddeman b. 1834 to Benjamin Haddeman. I found a Harry Haddeman who died in Blanco County, Texas in 1869, killed by indians. It is proving difficult to connect the dots in the middle.