Yes. I’ve had reports that the app works with external GPS receivers and I’ve recently bought a Garmin GLO Bluetooth Receiver to test DigiHUD’s support for these devices. From my own testing I’ve found that the app works perfectly at a refresh rate of up to 10 times per second.
How well it works will depend on factors like the speed of the device running the app and the speed of updates that Bluetooth can handle. I’ve found that even on an old HTC Wildfire S it keeps up with the GPS updates without issue.
The Pro version is currently being updated to indicate when external data is being used, or GPS data from the internal receiver.