Whether the individual files reference other parts of the site relatively (locally) or absolutely (eg. http://otherpage.com) is entirely dependent on the person who wrote the code, so it would be hit-n-miss.

I believe you can use a tool like wget to mirror a site locally. There are also options in the full version (I don't know about the busybox one) that will direct wget to actuallt fix absolute references to relative ones automatically. So maybe that would be your best option. But unless busybox supports those kind of options, you'd have to save the sites on your PC then transfer them to the NIT.