Good find. Yes they are spot on for O. polyphemus, judging by external appearance. As you say, the question is about their natural range. This is the least well documented part of our science In Australia, due to the incomplete way various databases and portals get their information. If you went to the WA museum, I'm sure you'll find hundreds of specimens of salticids identified only to genus, if that, and surely this species, recorded as Opisthoncus polyphemus? these records not being enough to tie down a species to a location. I will extend the range in the web site and the book. I see no reason for it not occurring naturally there, many others do which aren't yet 'official'.