Yes, you can do this since it is only an amplification circuit. About the worse that can happen is the amp will be a little quieter, but probably not enough to notice.
In a similar vein, Williams sound boards require +12V & -12V from the power supply for the amp (24V), but if you use a newer arcade switching power supply, you only have +12, +5, and -5V per the jamma standard. In this case, I wire the -5V to the -12V input to the sound board, and it still works fine. It just won't as loud as it would with -12V.