Is it possible to include and use Angular.js as part of a web app served using HtmlService in Google Apps Script or will caja sanitise it out?
Additionally will it be possible to use Angular within the HtmlService templating method within Apps Script itself?
You can use angular with following change in your appscript file.
var ui = HtmlService.createHtmlOutputFromFile('myPage')
.setTitle('My Title');
ui.setSandboxMode(HtmlService.SandboxMode.IFRAME);
This is not currently possible, although it may be supported in the future.