I got it to work with the <script>
tag syntax shown in Dojo documentation:
<script data-dojo-config="async:1" src="/xsp/.ibmxspres/dojoroot/dojo/dojo.js"></script>
The <script>
tag syntax in my question is a copy paste from this Dojo sample. Interestingly it does not work in Domino. Maybe it requires Dojo 1.8.3.