title sais it all... might be a dumb question, but VRX was from TJ onwards. will VRX flares (www.carmate.com.au) fit onto a 1999 TH Sports?

Yes they will

Don't forget that they are designed to 'mate' with the VRX front and rear bar extensions as well as the side skirts so would probably look odd without the rest of the kit.
Another thing to consider is if you decide to add front and/or rear(bumper) spoilers or side skirts you will need to use VRX ones to suit the flares. The GE and Ralliart flares are different again.