The SPF/DKIM is set at the DNS record level, so Kenny's right that for the client side, you don't need anything.
But I've setup this before on Gapps, and you DO need to verify that your DKIM/SPF record is set for the Google Apps as an authorized sender (which has nothing to do with Marketo)
....and to make sure your other settings did not change because of the migration. It's *possible* something could have changed on your end that will require a minor change to the DNS record for the Marketo SPF/DKIM authorization.