Quarter sawn is good, but flat/back sawn works as well just watch for grain run off, the less run off the better.
dont know if this is necassary for a backed bow
i have made a few boo backed hick bows that the grain was horrible(i mean HORRIBLE ) in the hickory
runoffs all over the place,they are still shooting.i have one yet as my own bow.crappy piece of hickry backed with an uneven (in thickness) piece of boo
i made this to show that the back nor the belly had to be "primo" pieces to make a bow from