There should be no problem doing what you described, in most cases. It works when I try it.
One way it might fail is if the type is not only rasterized, but also in bitmap mode (Image > Bitmap), which would be 1 bit per channel. Filters generally require at least 8 bits per channel. If you’re working with a 1bpc/Bitmap document and you want to apply the filters, first choose Image > Grayscale and then the filters should work.