Hardboard, is high density fiberbord (MDF is medium density) it is created with higher heat and pressure resulting in the darker color compaired to MDF. I have only found it in 1/8" and 1/4" thicknesses. I use hardboard for a few things around the shop. I have kids use it at school for practice scrolling because it is cheap. The top surface paints well, kids like that also. I use it often for making templates that will be traced. I also use it as the back of picture frames when we make frames at school.
I don't specifically remember a time when I used it as a backer for a scrolled piece, but I think it would work just fine.