Yes, you could do this. See developers.marketo.com or if the object exists in SFDC, you can ask it to sync in Marketo.
Why not just use the SurveyMonkey integration?
Marketo--as I've been told--cannot write from responses to custom objects. The SurveyMonkey integration is likely a good option. In addition, Marketo has the ability to leverage their custom object technology called Mobjects that can be associated with their lead table; essentially a place to store the survey responses--but this does require coding to build. Additionally Mobjects cannot be made visible in SFDC.