As in the title. From a flavor perspective, it sounds questionable. From a rules perspective, Apsu's Shining Scales has the "good" and "draconic" descriptors. Can an evil dragon cast a "good" spell?
Would they? Probably not, but nothing restricts Arcane and SPL casting like alignment based divine casting does. They could cast it as a divine spell if they were a Any Good/True Neutral aligned chromatic dragon (having undergone some level of redemption) worshiping Apsu as having become not evil, they now can receive spells from Apsu.
Many spells are questionable from a flavor perspective, but the rules allow it. This spell explicitly makes such a weird flavor choice by giving the spell to Oracles:
Clerics, inquisitors, oracles, paladins, and warpriests who worship Apsu add Apsu’s shining scales to their class spell lists as a 3rd-level spell.
Apsu has no oracles, for he believes inflicting a curse on a living creature is a terrible crime against that being, even in exchange for divine power.
Also, nothing stops the rules from applying to a different universe's pantheons, so a stand in for Apsu could totally have oracles.
Nothing says they can't, it's not a deity specific spell and dragons don't care about alignment descriptors.