Hello Bec,
I'm part of Marketo's Privacy Team; we handle deliverability and compliance. I haven't seen any evidence that using different From: and Reply-to: addresses will affect your deliverability, particularly when they're at the same domain. That said, you should be aware that autoresponders (such as out of office notices) generally go to the From: address, and many email clients give a responder the choice of which address to reply to. There's nothing wrong with using different addresses for each, but just be aware that the From: address will still probably receive some replies.