按照你的做法没有错啊？我是这样试的：

a.tpl

 <div class="widget">
  <div class="widget-title"></div>
</div>

webpack.config.js

 'use strict';

var path = require('path');
var webpack = require('webpack');

module.exports = {
    entry: {
        index: './index.js'
    },
    output: {
        path: path.resolve(__dirname, 'build'),
        filename: '[name].bundle.js',
        chunkFilename: '[id].bundle.js'
    },
    module: {
        loaders: [
            {
                test: /\.js$/,
                loader: 'babel'
            },
            {
                test: /\.(tpl|ejs)$/,
                loader: 'ejs'
            }
        ]
    }
};

index.js

 var tpl = require('./a.tpl');

console.log(tpl());//<div class="widget"><div class="widget-title"></div></div>

require('./a.tpl') 返回的是一个 compiled template function , 执行一下这个 function 就好了

你是 ejs-loader 报的错？