The reason PayPal Pro was recommended back in that old thread has to do with whether or not the buyer is automatically directed to your thank you page to trigger the referral tracking. If the buyer is not automatically sent there and doesn't have a reason to bother visiting your thank you page that might cause some referrals to go untracked.
If you are selling digital products that the buyer will be downloading from your thank you page you don't need to worry, they have to go there to get their product and that means you can count on the tracking to work properly.
If you are not selling digital products then PayPal Pro isn't even the best option to ensure that buyers are directed to your thank you page automatically, because that would only happen when the buyer paid through the credit card checkout page and not if they used a PayPal account. The other processors we have that will automatically redirect are Authorize.Net, ClickBank, & 2CheckOut.
Of those Authorize.net would give you the most options, ClickBank and 2CheckOut only have a limited integration with us... ClickBank is best for their affiliate program (and you are already using iDevaffiliate) and 2CheckOut is only best for merchants who are in a country where they cannot get service from one of the other major processors.
The key is getting the buyer to your thank you page one way or another, even if your payment processor won't automatically redirect them you just need to find a way to compel them to visit with some kind of important information or special deal.