crates.io handles path dependencies by handling them as if they point to the crates.io version, e.g. if ioreg is version 0.1.1 and platformtree has [dependencies.ioreg] path = "../ioreg" that will effectively be rewritten to
[dependencies]
ioreg = "0.1.1"
This does mean that all have to be published on crates.io.
(I'm not sure if this is what you mean?)