PhotoPost Pro has the "portal" configurable front end already; there are some skins for it included, but you'd have to do a little work if you wanted to use a vB skin on a stand alone.
I even modified the front end on
http://www.shutteralley.com to remove the forum listings and just display recent photos added.
I did use a vB skin on one site by purchasing a second skin license and then copying the header, headerinclude and footer scripts (along with the css file) from the vB site to the standalone files header.html, headtags.html, footer.html and style.css. Worked like a charm without needing vBulletin to be installed.
[I did change the photopost forum file to use vB style names versus the PhotoPost internal ones and used the non-vB PhotoPost templates.]
That's how I got a vB skin to work on a stand-alone copy of PP anyways.