I don't know if using Hammer JS is a requirement for you but I've had success implementing horizontal scrolling (and disabling vertical scrolling) in iOS with iScroll 4 https://github.com/cubiq/iscroll (Examples here: http://cubiq.org/iscroll-4)
When you invoke iScroll, in the options pass hScroll: true and vScroll: false, like so:
new iScroll('XYZ', { hScroll: true, vScroll: false });