Then there's other tricks you could do like port forwarding, filesystem mounting over SSH (sshfs) etc. But if zmodem works for you then it's as good a solution as any of the above. I only give SSH examples as demonstration at just how scarily powerful a tool it can be.
That assumes ssh is present to begin with. Really in the embedded world (which was the context if I got it right) you can just about throw all those assumptions out of the window. You're roughly back in 1989 or so when it comes to the features available to you in the environment, unless you're going for the more powerful platforms (with associated physical footprint, power consumption and boot times).
