Have you enabled the "Primary Only" option? Then disable this option:
Then only the primary selected image will take changes made in the Browser, see this user tip: Keywords or ratings are applied only to one of the selected images - why?
I have not yet noticed a difference between raw and jpeg with this option enabled. Do you see this when using "Batch Change" and applying the changes to the original files? What is your Aperture version? Batch changing has been buggy in this respect in earlier Aperture versions.
Primary only is not image type specific so unless you change that setting between keywording operations it is unlikely to resolve this.
Could you explain in more detail just what it is you tried on both the Raw and JPG images? Are the JPG images imported from the camera or were they brought into Aperture in some other way?
Are these images part of a Raw & JPG pair?
In addition to the keyword issue, I noticed in the Info brick that the EXIF settings (including lens info) wasn't carrying over from the camera. My Library, incidentally, is Referenced.
So I trashed all the imagines, and then re-imported them from an external disk. The EXIF info carried over.
I then did a drag & drop method of adding keywords, and everything worked well. I tried this both in Browser Mode and List View. So, the only thing I don't know at this point is whether Batch Change will do the same. As soon as I import some new photos, I'll try that.
This problem might have arisen a month or so back when I switched from a Managed Library to Referenced. Due to surgery, I haven't taken any pictures since June. That's all over now and I'll be out with the camera.