Using Vagrant, we can still:
* Write software that depends on POSIX-only applications, such as Redis and, yes, Docker
* Share development environments-that-look-like-production with other developers, thus avoiding "works on my machine" bugs.
You need very little Linux knowledge to do this. Just apt-get, a text editor and the occasional HOWTO/blog post gets you very far.
Additionally, with Docker-on-Vagrant, we can easily:
* Simulate a multi-server environment locally without hogging resources
* Do effective versioning on dev environment configuration before sharing stuff with colleagues
* As a result, learn Linux administration with easy rollbacks after fuckups.
All this without an on-team Linux guru.
Of course, once you go live, you'll need a decent sysadmin/devop type to un-suck the installations. And backport that to the dev setups. Or, just go to some PaaS and have the security/efficiency part done for you. But that's not my point: my point is that even without running your own hardcore-linux-guru-devopsed production environment, and without anything more than basic Linux skills, you can get a lot of value from Vagrant+Docker.
And it is growing more and more common that most developers in larger organizations don't even know Vagrant is being used under the covers because it is being masked by higher level scripts ("click button to start dev environment"). Under NDA I can't say any names here, but it is more common than you think.