[GPSNavX]

It appears Safari in iOS will display any XML files as basic text, but will pass binary files such as GRIB and KMZ onto apps. So suggestion is to use KMZ files to store routes, waypoints and tracks if you want to access them from a website.

I do note that linked (download button) KML and GPX files on X-Traverse.com can be opened in iNavX. Must be some backend server processing that makes it work.