Yes, an imported RAW file will be saved as a RAW file. Photos is always keeping the originals stored in the library. and when you apply adjustments, they will be applied, starting from the saved RAW image.
The option "Image > Use Raw as original" is only available, if you are importing RAW&JPEG pairs. With a RAW&JPEG pair, you have two original image files, and then you have to tell Photos, if you want to apply the adjustments to the RAW file or the JPEG. The "Image > Use Raw as original" option will then become available, if you open the pair in Edit mode. In the browser it will always be dimmed.
But when you edit a photo, the edit version will not be a RAW. file. After photos applies adjustments, it has to render a new file for the exported, edited version. In the "File > Export" dialog you can select the file format you want - JPEG, TIFF, or PNG. Or use "File > Export > Export unmodified Original" to export the unmodified RAW file.