As long as the remote device supports Bluetooth Serial Port Protocol (BT-SPP) and supports pairing, you should be able to open a BT-SPP socket to it from WP8.
Here's a code sample of connecting to Sphero @ http://www.developer.nokia.com/Community/Wiki/What%27s_new_in_Windows_Phone_8#Bluetooth:_Phone_to_device
And here's a code sample of connecting to Mindwave Mobile Headset @ http://metroeeg.codeplex.com/wikipage?title=Standalone&referringTitle=Home