Rotated axis tick labels are possible through the "jqplot.canvasTextRenderer.min.js" and "jqplot.canvasAxisTickRenderer.min.js" plugins. Native canvas font rendering capabilities are used in supported browsers. This includes most recent browsers (including IE 9). In browsers which don't support native canvas font text, text is rendered in the Hershey font.
For comparison, here is the same graph with the "fontFamily" and "fontSize" set. If you have a supported browser, you should see a difference in label fonts.
The default positioning applies to either primary or secondary axes and accounts for label rotation to ensure that the labels point to the appropriate bar or tick position.
Also note here the use of the "autoscale" option on the y axes. Turning this option on will force the y axes to line up tick marks for consistend grid lines across the grid.
You can override the default position by specifying a labelPosition of 'start', 'middle' or 'end'. The results probably are not as pleasing as the default 'auto' setting.