Hi KC,
This is a good way to go but the implementation is a little tricky. You will need to learn the SFDC Id of the 2 record types so that you can set them from Marketo. It will take the form of "0012000000eYIIfadC". When you will want to set the record type, you will have use these as the new values. As it is easy to make mistakes there, I strongly recommend that setting record types is done in a centralized program that only experiences Marketo users are allowed to touch and edit. Another possibility would be to have a user-readable picklist field in SFDC (name it "Requested Record Type"), map it to Marketo and have a workflow in SFDC that changes the RT when the field is updated from Marketo.
Also, I recommend you create a formula field in SFDC on the lead object called "Record Type Name", so that you can easily check the record type of a lead. The formula for this field is : RecordType.Name The field will give you actual the name of the RT in a way that is understandable to a mere human being 
-Greg