Does the Affiliate plugin need to use the wp-signup.php page to track referrals

Howdy all,
I may have missed this when I got distracted by something sparkly, but just wondering if the affiliate plugin needs the referrer link to go via the wp-signup.php page so I know who to share the booty with, or can I use a custom registration page. I'm currently using gravity forms for registration but starting to see some cracks and may have to let out the code monkey.
Thanks in advance
D