I downloaded the latest AddIns sample from GitHub, loaded the CS solution, set SolidEdge.AddIn.EdgeBar as the primary project, built everything, ran the Registration.bat under the EdgeBar project, and picked register 64bit. Started SolidEdge ST7. Opened the Add-In Manager dialog, and "CodePlex EdgeBar AddIn" is checked. The file referenced is the one I built. Loaded a part. Here the Edge Bar has the normal stuff like Feature Libary, but does not have AddInDemo as one of the tabs. Also, the debug output does not mention loading SolidEdge.AddIn.EdgeBar.dll. What's gone wrong here?
If you'll click the Download ZIP button on GitHub, you will get the absolute latest samples. Once downloaded and extracted, you can find the C# example in .\cs\SolidEdge\MyAddIn. I have also previously posted a blog with a video on how to create your own C# addin from scratch.