USB bluetooth should work fine, normal Mac's have PCIe Wifi and USB bluetooth cards.
The one is use is the BCM94352Z:
View attachment 112698
As you can see from the connector strip, the left hand side lanes are PCIe for Wifi, the middle lanes are unused (So no SDIO interface) and the right-most lanes are USB for Bluetooth.
Here you see a sample Intel WiFi card with PCIe and USB connectivity lanes marked for reference:
View attachment 112703
Additionally in System profiler it shows up under USB and under Bluetooth shows as "Transport
USB".
View attachment 112699
So the following needs to be true:
- Bluetooth device should support Bluetooth 4.0 + Low Energy
- Bluetooth device should have LMP version greater or equal to 6
- Bluetooth device should have appropriate firmware loaded (Google Bluetooth Firmware Uploader)
- Hackintosh SMBios platform is whitelisted for Hand-off / Airdrop
- If using a non-Apple branded bluetooth chipset (I.e. Vendor ID is not 0x05AC), then the IOBluetoothFamily.kext patches are needed to ensure getCapabilityFlags() of the BluetoothHCIController returns 0x0F (All flags enabled).
So theoretically any compatible USB would work, since OS X does not seem to be checking what internal or external USB bus it is connected to.