Not really, no. Splunk's dashboard mako template doesn't have any concept of rowspan.
However you can hack things a bit with custom CSS and sometimes this is good enough.
Splunk's docs for using Custom CSS are here. http://docs.splunk.com/Documentation/Splunk/6.0.2/AdvancedDev/UseCSS
Setting one of the modules on the left side to have a larger than necessary height, would of course push down the left hand side modules that follow it.
one advanced note: Ordinarily in core advanced XML you'd have to use the module id attributes and these will change the next time the view is edited, breaking all your CSS. So instead you can also use the "cssClass" param that all Sideview modules have, and this can make for a less brittle linkage between the XML and the CSS.
