Dojo is a cross platform API and on IE8 and below it generates VML, elsewhere (e.g. IE9+) it generates SVG.
- Microsoft's VML is limited to these combinations and therefore, to work cross-platform so is dojo.
- You could work around this by generating custom SVG stroke styles directly but they wouldn't work on IE8 and below.
- Not with VML, it is possible with native SVG though.
e.g.
<line stroke-dasharray="5, 5"/>
<line stroke-dasharray="15, 15"/>