To use PayPal Website Payments Pro as a payment gateway and handle recurring donations you need to ensure the IPN is specified in your PayPal Pro Business account.
Log into your PayPal Website Payments Pro account,
Under My Account, goto Profile, My Selling Tools.
Under "Getting paid and managing my risk", click on the Update link for 'Instant Payment Notifications'.
In a separate web browser window, goto your RaiseDonors account and navigate to Account Settings - Merchant Settings - Merchant account & payment gateway (link here)
Copy the silent post url from RaiseDonors into PayPal's Instant payment Notification text box.
Note, if the IPN is in use for a different integration/purpose, your recurring donations will still work. But, the charge from each instance of the recurring profile will not be reflected in RaiseDonors.