If, when you manually ssh to those other machines, you have to type in a password, cron is going to throw up because it isn't set up to give that kind of input. There are ways you can set up ssh to not need to supply a password (RSA keys or something, I don't know for sure, go read some man pages or websites).

Of course, you could write a wrapping script in Expect¹ to take care of that pesky problem, but that's probably Not The Way To Go.

¹ Yes, I know I will burn in hell (and get downvotes) for mentioning another language here, but this kind of tty-needing, input-needing interaction is just what Expect is for.