Hey Scott, I don't know exactly about the conditions in August, but the track up there is very wide and easy. I think it's been used by some sort of vehicle (tractor or 4wd), although it looks a bit overgrown now. But I can't guarantee that it will be easy / safe etc. In any case, always bring some extra warm and windproof clothing, as the NZ weather is very changeable. But the best thing to do is contact the DOC, they'll be happy to tell you.
When you obtain this information, would you mind posting it back here, or on the <a href="http://www.summitpost.org/show/mountain_link.pl/mountain_id/6317">Roys Peak</a> page as an addition (as a matter of fact I maintain that page and I'm ashamed that I don't know conditions other than in summer)
The appropriate DOC office is:
<ul><li><b>Mt Aspiring National Park Visitor Centre</b>
PO Box 93, Ardmore Street, Wanaka
ph (03) 443 7660
fax (03) 443 8777
e-mail:
wanakavc@doc.govt.nz</li></ul>