Will this work with my existing mirror housing?

Yes. This lens is designed to drop into the OE mirror housing using factory tab mounts. No drilling, no modification to the housing itself.

Do I need to remove the whole mirror from the door to swap the glass?

Most installs pull the glass directly from the housing with the mirror mounted. Check your specific year's manual—some trim levels allow mirror-on-door removal for easier access.

Is this a raw lens, or does it have a backing?

This is the complete glass assembly with its factory backing intact. Install straight into your housing.