But I worried that would mean search engine bots couldn't index my site so I turned it back off. Would your mod have the same problem?
No. Search engines would still be able to crawl the pages normally. My mod just blurs the content on the client-side via CSS.
And what Dave said, I would move the content to the root of the url. No need for that useless landing page. All it does is to add an extra click to get to the actual content of the site. But when you do this, you have to redirect all requests for /vBulletin to /.