Going wireless with Skype for Business WITHOUT a dongle?

If the Bluetooth headset is AVRCP capable and the computer is running windows 10 creators update (which I believe baked AVRCP into windows) then I believe it should work. I have certainly been able to answer SfB calls by pressing a button on my Bluetooth headset. Unfortunately I broke the headset so I don't have one to hand to double check but I am 95% certain that for answering an incoming call and controlling call volume it worked fine.  Anyway, your starting point is to look up AVRCP.

I agree with you re the benefit of using a Bluetooth device - less to get tangled up, snagged or broken (unless like me you sit on the headset). You may find that SfB reports poor audio quality. This is because Bluetooth uses a lower bit rate but if it is subjectively ok for you then just ignore the warning - I couldn't really tell the difference between Bluetooth and wired and the benefits of Bluetooth outweighed the (theoretical) audio quality issue.