While waiting for much more qualified respondants I would be very surprised if it was used. In general, viffing was used at fairly slow speeds to use bleed air (through reaction ducts) to give monentary enhanced nose authority. It came at the expense of instability and loss of overall energy. From all reports I have read of Falklands combat the engagements were all fairly high speed and I can’t see viffing being of any benefit. Not a SHar expert though so I standby to be corrected.