Note that Hype v3.5 (released a couple months after this post in Dec 2015) introduced a way to easily include the system font:
This is an equivalent to CSS:
font-family: system, -apple-system, ".SFNSDisplay-Regular", "Helvetica Neue", "Lucida Grande", Helvetica, Arial, sans-serif;
Therefore for most cases you will not need to manually include the SF font.