Can DDC of another brand be used on Denafrips Dac?Audio GD etc

If you’re planning on using the i2S connection via HDMI you should check for compatibility as there’s currently no standard pin configuration.  You’re safer using something like a Denafrips Hermes or another Denafrips model, but the Audio-GD might work.

It will work with the Matrix i2s.

No experience with the Audio-GD  DI-20HE (it looks awesome, btw!), but I have successfully used a Holo Audio Red in DDC mode, feeding it USB to convert to I2S for a Pontus II. I have the Iris as well, and it's great, but I was curious about I2S output at 768k/24, which the Red supports. 

Both the Audio-GD and the Red have adjustable pinouts, and the Denafrips DACs also have adjustable pinouts, so I suspect you would have no problem.