The DMG outlines what it means to be a spellcaster:
If the prerequisite is to be a spellcaster, a creature qualifies if it can cast at least one spell using its traits or features, not using a magic item or the like.
The requirement to cast spells from scrolls as referenced by the Spell Scroll magic item (DMG pg. 200) says:
…if the spell is on your class’s spell list, you can use [it]…
But creatures don’t typically have spells lists as they have traits or features for casting spells.
Does that mean that no creature is able to cast spells from scrolls even those categorized as spell casters? What creatures can cast spells from scrolls?
Note: This question differs from Who can use magic scrolls? as this question pertains to creatures specifically which that question does not address.