Now that you can sign up for Netflix with your Apple ID and use that for billing, does that allow you to get it billed to your iTunes Credit rather than credit card?
According to this Bloomberg article:
More details and support links can be found on Netflix's iTunes billing page.
Finally, according to the current US iTunes terms and conditions:
While the current T&C doesn't directly mention the Netflix subscription situation., the iTunes Card ("credit") comes before the credit card or PayPal account. However, since Apple also has your credit card information, as this Fast Company article notes, your credit card might actually be used to pay for your Netflix subscription instead of the iTunes credits.