So Making an actual Gameboy game if you dont already know is going to way more difficult then just using something like Unity or game maker. There are less resources in terms of documentation and help and it is much more complicated then modern engines.
Ask yourself what it is you want to achieve in the jam - is it to make a cool game? if so, then do that in the easiest, most empowering way and make something really unique
If it is to learn how to make an actual game boy game then great! But you probably wont be able to do that AND make a good game in all likely hood and you would probably do better taking longer then a jam to learn actual hardware.
I hope this helps!