Double SC on TT flights I assume also between NZ and Australia (reverse order)
 

Terms & Conditions:

To be eligible for the Double Status Credits promotion you must
(1) Activate this offer through the activation link contained on this page between 12.01am AEST 13 November 2018 and 11.59pm 14 December 2018 inclusive (Promotion Period);
(2) book an Eligible Flight during the Promotion Period; and
(3) enter a valid Velocity membership number at the time of booking.

An Eligible Flight is any flight between Australia and New Zealand marketed and operated by Virgin Australia for travel between 26 November 2018 and 9 October 2019 inclusive.

Only flights and fare classes that normally earn Status Credits are eligible for earn on this promotion. Changes to existing bookings made prior to qualifying period are not eligible to earn on this promotion. Bonus Status Credits will be applied to the originally purchased fare class and any upgrades will not attract extra Status Credits. This offer cannot be used in conjunction with another bonus status credit offer by Velocity Frequent Flyer or Virgin Australia.

Status Credits cannot be earned on Velocity Reward Seat bookings. Where multiple guests are listed on the same booking, only those guests who have entered a valid Velocity membership number and have activated, booked and flown within the qualifying period are eligible for this offer. You should allow up to 4 weeks after your eligible activity for the bonus Status Credits to be allocated. To earn and redeem Velocity Points you must be a Velocity member. Velocity membership and Status Credit earn are subject to the Member Terms and Conditions, as amended from time to time.

"Between" sounds like it means either way. If it was one way the terms would state "From Australia To New Zealand".

I'm pretty certain double status credits would apply both ways, assuming you are flying on VA metal.