You can do pause and volume up, but you have to do them through an activity, and it can be quite awkward.
I do this because I am quadriparetic (use a wheelchair and have limited hand function) so totally hands-free control is of great benefit to me. But I would think most people with more hand function would prefer to just use the buttons on the physical remote for volume.
Also, because harmony will not let you do the same activity twice in a row, I have to have two activities for volume up and two activities for volume down and switch back-and-forth between them.
The following topic does discuss how to set up these type of controls so totally hands-free control is of great benefit to me.