I don't trust most air purifier manufacturers. They totally would add a fancy-sounding feature which sounds good, even if it has negligible effect, or even negative effect. Case in point: they're still pushing ultrasonic humidifiers.

The tiniest particles aren't necessarily the most dangerous, so even if "clumping" worked as advertised, it wouldn't necessarily be good. Air filters are worst at filtering particles at about 0.3 microns, they're better at filtering smaller ones (I understand it has something to do with brownian motion). I wouldn't be at all surprised if a similar thing affected our biological "filters". Either way, if you have a filter, you don't need UV to clean air. Just push more air through it if you need cleaner air faster.