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.