I believe that it would be better to explain to the group why you've chosen to use a framework, and why you've selected React (as it seems you have). The reasoning should be project-based, not based on the utility to the group later in the job market. Learning vanilla JS is not, as you suggest, less valuable than learning React, or some other framework. Neither in general, nor in the job market. There are needs for programmers who can do vanilla JS and those who are fluent in React.js - and Vue.js, Meteor.js, Backbone.js, and Angular.js 2, among others. Which ever framework you select might not be any more valuable, eventually, to the students' future than vanilla would be.
The reasons to use a framework, when you do, can include the points you've already mentioned. If those are points which are important to the project. The issue of learning multiple things at once is not really an issue. First off, they are already learning several things - HTML, CSS, design, UX, and probably some of the aspects of the server setup and maintenance. Whether they are learning vanilla JS, and how to keep everything working and bug free, or leaning a JS framework becomes insignificant.
The final question would the project better reach it's goals by using a framework, or not? isn't something that can answered anonymously. It is something which has to be evaluated in context for the project itself. In this case it seems the "project" has two objectives: the finished product and the learning of the group.
Using a JS framework vs vanilla JS is similar to planning a road trip to Miami. There are many routes that will get there. It isn't even necessary to use a map. You can keep picking your road by knowing that you want to go east and south. Eventually you will get there. There may be some excellent scenery along the way. There may also be a few detours, road blocks, and dead-ends. How you choose to plan, and which roads you use, depends on the purpose of the trip. If the point is to see the country between here and there, taking country roads and scenic byways with little pre-planning could be the best option. Anything goes, and you can pick any road, stop anywhere, and do anything you want. If, on the other hand, the point is to get to Miami for Spring Break, a better choice might be to use a map, travel on Interstate highways, with targeted stop-over points each night. Using the first, free-form, method could make you late for the party. Maybe even not get there before it was time to head back for classes after the break. The Interstate system is the "framework" which has been built to make travel easier. It's not always the best choice, it's only one of the choices, and serves well for one of the possible purpose of a road trip.
Knowing that there are options, and how to select between them, could be more important than the choice you make for the current project.