Does all this means that a faerie dragon
- can cast scrolls and wands with spells from the sorcerer/wizard list without doing a UMD check?
Yes. Wands can be used automatically with no difficulties whatsoever; scrolls work as the faerie dragon either has a high enough caster level for the spell, or succeeds on a (relatively easy) caster level check.
- has to perform an UMD check for all other spells not on the list?
What does [“the user must have the requisite ability score”] mean for scroll and wand activated spells from the sorcerer/wizard list?
This... is actually somewhat contentious. Spellcasters require a certain ability score in order to cast a spell, e.g.
To learn or cast a spell, a sorcerer must have a Charisma score equal to at least 10 + the spell level.
To learn, prepare, or cast a spell, the wizard must have an Intelligence score equal to at least 10 + the spell level.
The problem is that it’s unclear which requisite ability score is relevant. If a wizard wants to cast a 3rd-level spell from a scroll scribed by another wizard, he needs Int 13. But if a sorcerer (or faerie dragon) wants to cast that same scroll, does he need Int 13 (which would be the requisite ability score for the wizard who originally scribed the scroll) or Cha 13 (which would be the requisite ability score for the sorcerer to cast the spell himself)?
Summoners get even more confusing, since they have spells at different levels: does a wizard-scribed scroll of haste require Int 12, Int 13, Cha 12, or Cha 13? After all, summoners have haste as a 2nd-level spell, so they require Cha 12 to cast it themselves, but it was still scribed as a 3rd-level spell by a wizard who needs Int 13 to cast it.
The general consensus, from a quick Google search, seems to be that you need the ability score that you would need to cast the spell yourself, not whatever the person who scribed the spell would have needed. The primary reasoning for this is that in all published adventures, you see loot like scroll of haste, not scroll of haste scribed by a wizard or whatever. On the other hand, there is a rule to assume cleric, druid, or wizard made magic items that don’t say, so that argument is not all that strong. It’s just the best we have.