open command on Linux is unrelated; it is (on most distributions) another name for
openvt, which starts a program in a new text console (a feature that isn't used much nowadays).
The command corresponding to OSX's
open, on a modern Linux system, is
xdg-open. However, that would open the file in a program running on the remote Linux machine, not locally on the Mac.
SSH provides a way to run remote commands from a remote prompt. It doesn't directly provide a way to access remote files. Most unices, including OSX, allow a remote directory to be mounted over SSHFS. You can create a directory on the Mac, say
~/ubuntuserver, and make the remote files accessible under this directory:
sshfs ubuntuserver.example.com: ~/ubuntuserver
There may be a Mac GUI for that (I wouldn't know).
To avoid authentication hassles, it is recommended to use a public key for authentication, and if your SSH is recent enough to support it, to activate master/slave connections in