The Plastic plug-in supports the following Authorize.Net services: Automated Recurring Billing (ARB) and Customer Information Manager (CIM).
With ARB, you enter the parameters of the subscription (start date, recurring amount, frequency, etc.) and Authorize.Net takes care of the rest. When you create a subscription, you get an ID in return that you can use to update certain aspects of the subscription or cancel it, but you cannot get transaction feedback via the plug-in.
With CIM, you create a customer profile and then you can create one or more payment profiles tied to that customer. When you create a customer profile, you get an ID in return that you use to create a payment profile. When you create a payment profile, you also get an ID in return. You use the combination of a customer profile ID and a payment profile ID to perform a transaction on demand, for which you will receive response feedback from Authorize.Net.
Since CIM gives you the ability to perform a transaction on demand, you could roll your own recurring mechanism purely in FileMaker and use the plug-in to perform the transactions scheduled for a given day in a looping script. That way you could record the success or failure of each transaction and any auxiliary information directly in the database. It's certainly more work, but it gives you feedback that you won't get using ARB.