In reading up on some lenses, there are some with bad barrel and CA issues. I know the GH3 corrects for them shooting stills but what about shooting video?

The GH3 makes automatic corrections in video mode, but I believe only for Lumix lenses.

If you shoot stills in Raw and then convert straight to Tiff file it will provide an image that has not been corrected. This will result in a larger image with more pixels compared to the corrected image. For example, a 14mm or 7mm lens will provide a slightly wider image.
Quite a lot of the original view is lost during the correction. I sometimes use the uncorrected image when I require to include important aspects that are at the extreme edges of the frame, but Silkypix editing software will quickly re-correct the Raw file whenever needed.