i2c uses GPIO3/2 (clock & data). My take on this is: at boot certain software may use i2c to detect and configure boards (automated devicetree detection thanks to EEPROM read for instance), but that’s at a time where, if you connect a push-button, that part of the wire will be “up in the air”, and not shorted to GND by the button. So I do not anticipate this may cause any trouble (but I take no responsibility if it does of course).
Volumio does have it’s own (more complex) DAC auto-detect procedure which does use i2c too, and interaction with such use of GPIO3 is discussed here.
The discussed case is different: unwanted error messages happen when no HAT are connected to the Pi. I do not think the same (non-critical) thing will happen in your case because HifiBerry board does connect GPIO3 (hence no clock stretching phenomena).
In any case, should auto-detections even fail, you may set audio-out device with UI and save config, so it should not adversely impact your setup I guess.
Your call, but if you decide to try, thanks for posting your feedback.