Technically if you bolt your new seats to the OEM rails and use the OEM seat anchor points, you shouldn't require a cert. If the WOF person, in their opinion is happy that your seats are safe and secure, then no problem.
But like anything, if your workmanship is bogey and you fit some seats to some whetu as rails and drill some holes in the floor to mount it, the WOF man's going to send you on your way to get a LVC, which you will also fail.
Check out page 4 of this document:
http://www.lvvta.org.nz/CertThresholdScheduleApril04V3.pdfI have been know to take this document with me when getting WOF's
