Some dragons can cast spells that are clearly on the Cleric's spell list. Despite that, do they always count as arcane spells when cast by a dragon? For example, see silver dragons cast stuff like Resurrection and Cure spells.
The bestiary entry for dragons says they cast arcane spells, so they cast arcane spells. Spell-like abilities depend on what list they appear on primarily, but in the case of those spells, they are arcane even though a PC could only cast them as divine spells.
Edit: In the entry for silver dragons it has this footnote: "* A silver dragon can cast cleric spells as arcane spells." So, yes.
