Can you publish in HTML5 in Articulate Storyline 1?
yes - here are the technical specs for SL1 and the tutorial for publishing to web
It's also worth noting that within Storyline 1 and 2, if you include the HTML5 as a part of the published process it will still include Flash files as well. So the HTML5 output will only be accessible on devices that don't have Flash (such as iOS mobile devices for SL1) or desktop browsers such as Chrome.
If you're looking for HTML5 only as a publishing option that is available as a part of Articulate 360, within Storyline and Studio.