You can import from disk and import all the contents from that folder. Don't remember how it treats xmp files (which, presumably, is where your keywords would be?). If no xmp I'm pretty sure you'll have to re-keyword. (I can't imagine your raw files are DNG, but that would have solved the problem as well).
I only bring the RAWs into LR, not the subsequently processed images.
When I need to deal with a final image, Bridge is fine for me. (I print from Qimage) and use JAlbum for web, but if you want to print from LR our use their gallery functionality, you'll need the tiffs in LR as well (or maybe just new tiffs going forward).