Tape or corner bead where Hardi meets Drywall?
I had a similar situation where the backer board extended a few inches past my planned tiling edge in my shower. After I had finished with the tile, I taped the joint and applied joint compound over the backer board and it seems great. It's been three years and there is no cracking or any problem with it. That's not exactly an answer but I hope it helps you decide.