I don't have any experience with running Baldur's Gate in the Neverwinter Nights 2 engine (maybe its fantastic, maybe its not) but I really do not think that it is necessary. Baldur's Gate certainly has a dated UI and dated graphics, but Neverwinter Nights 2 is hardly recent... and Baldur's Gate is very playable even if you skip the Enhanced Edition.
In any case, you will need to purchase Baldur's Gate (I assume) even if you play it in NWN 2, so why not fire it up in vanilla first to see how it goes?
