Is there a reason for not using npm for dependencies? Do you gain something from using submodules instead?
As a developer, I don't want to install npm.
npm is part of node as of v0.6. Sorry you have no choice now.
+1 for npm
As a developer, I don't want to use Git. I usually use hggit to talk to Github, but submodules are not supported.
(I'm not trying to start a Git/Hg flamewar here; I'm just more comfortable in Hg.)
Depending on the version of npm you can put the ssh path or the tar path in your package.json file.
This project needs a lot of work before its useful as a node module though. You have almost no control because of the way things are structured. Its a direct port of a PHP library. I am working on a fork (pull request #23) that solves this but it is not finished yet.
jsDAV now uses NPM for all its dependencies.