if you are scraping and parsing anyway, it would be nice if your search engine was indexing the most common board objects... For example, the username, DT rank, feedback, boards,... That way, you could use keywords, like you can in google (filetype:, site:,...).
But this wouldn't be like rebuilding the full forum on a database?
I mean, there are 2 ways to do this:
1.- You take all the forum data, and put it together on a database and then your search engine makes calls to that database. But for this, you will have to live update that database or at least have a cron job to add the new data each x time.
2.- Search for the data directly on the site, but for that, you would have to do some kind of hack to the current search engine.
If you have other way in mind i would love to know how it work.