Skype with bluetooth headset on MacBook Pro
In Skype's Audio/Video preferences you need to see the microphone and speaker source to the BlueTooth headset in order for Skype to use them. So CMD-` to open Skype preferences, click the 'Audio/Video' tab icon and then check your settings.

In my own Skype install you can see I have to set it to use my Plantronics .520 headset if I want to use that for input or output: