Indeed, that is not handled by the search plugin.
Please change the line:
$rows[$k]->href = hikashop_completeLink('product&task=show&name='.strtolower(preg_replace('#[^a-z0-9_-]#i','',$row->title)).'&cid='.$row->id.$Itemid.$parent);
to:
$app=& JFactory::getApplication();
if(method_exists($app,'stringURLSafe')){
$alias = $app->stringURLSafe(strip_tags($row->title));
}else{
$alias = JFilterOutput::stringURLSafe(strip_tags($row->title));
}
$rows[$k]->href = hikashop_completeLink('product&task=show&name='.$alias.'&cid='.$row->id.$Itemid.$parent);
in the file plugins/search/hikashop_product.php and try again.