PP is the video editor of the suite, and is FAR more capable than what PS (and I assume LR) can do with video. It would make sense to learn PP if you intend to do a lot of video work.
What is LR4?
Photoshop Lightroom version 4.
I will guess it is this - http://www.adobe.com/products/photoshop-lightroom.html - edit - Jeff beat me to the click... but I have a link :-)
I will also guess the OP is talking about editing the individual frames of a video as individual pictures, and then using the results in PPro
I have never tried to edit individual video frames, so really don't know anything about the subject (is that rotoscoping ???)