I spoke with the developers.
For Win7, we do not have C#/VB.Net samples to access BTWLEAPI.
However, it should be possible to access BTWLEAPI.dll from C#/VB.Net.
For Win8.1 - C# Samples based on MS BLE stack are available here: http://msdn.microsoft.com/en-us/library/windows/apps/bg182882.aspx#four
Bluetooth device support
[Get the Bluetooth Rfcomm Chat and Bluetooth Generic Attribute Profile samples now.]