Rainbow Servant "cleric spell access" questions

[Nifft]

Would I be able to write cleric spells into my spellbook and then prepare them normally or metamagic'ed?

Yes.

And from the duskblade side, I'm assuming RAW I can't actually learn cleric spells for my spells known, but it seems like I could learn cleric spells from my "every odd level" swap?

You can learn Cleric spells for your spells known, and you can learn Cleric spells when you odd-level swap.