In case it's of interest to anyone considering converting Nectar to (now) LNER e-vouchers, the Nectar website continues to refer to Virgin Trains East Coast as of today.
The e-voucher codes do work on the (now) LNER website, as they should, and the confirmation email from Nectar has been updated to reflect the branding changes:
The e-voucher codes do work on the (now) LNER website, as they should, and the confirmation email from Nectar has been updated to reflect the branding changes: