Can I use an ES6/2015 module import to set a reference in ‘global’ scope?

Shimming modules is the way to go: http://webpack.github.io/docs/shimming-modules.html

I quote from the page:

plugin ProvidePlugin

This plugin makes a module available as variable in every module. The module is required only if you use the variable.

Example: Make $ and jQuery available in every module without writing require("jquery").

new webpack.ProvidePlugin({
  $: "jquery",
  jQuery: "jquery",
  "window.jQuery": "jquery"
})

To use this with your webpack-config just add this object to an array called plugins in the config:

// the plugins we want to use 
var plugins = [
   new webpack.ProvidePlugin({
      $: "jquery",
      jQuery: "jquery",
      "window.jQuery": "jquery"
   })
];

// this is your webpack-config
module.exports = {
    entry: ...,
    output: ...,
    module: ...,
    plugins: plugins
}