Users who register via RPX/Janrain Engage have to complete the same reigstration requirements as anyone who registers via the regular registration page. ie required custom user profile properties must be completed in order to activate the account.
However if you're doing something custom with Form Wizard Pro for site registration I have no solution for that to work with Janrain. Form Wizard Pro was never intended as a replacement for the built in site registration process.
Best,
Joe