As a happy Linode customer, I asked about their support team about the steps here. The response was positive and I feel belongs here:
Thanks for writing us. The pre-packaged kernels we provide do not support AUFS, which is a docker requirement. The guide that you’ve linked to walks you through installing a distribution-supplied kernel for your Linode, which is very much a valid operation on our platform. Running your own kernel will allow you the flexibility to use modules not present in ours.
We have also have a guide for installing a distribution-supplied kernel here (this guide does not proceed with instructions specific to running Docker):
I can’t comment on why Docker would require a larger swap file, but everything else in the steps you’ve found make sense to me. If we can answer any other followup questions, we’d be happy to do so.