Can I use ssh from a unix server to access Serv-U directly.

I have two users that are going to be accessing the Solar Winds Serv-U Server.  One want to use straight SSH commands from a unix based machine.  The other needs to use sftp from a different box.  I have been able to successfully set up the Serv-u to use Keys only (no username/password) for the SFTP user.  I have had NO success with the ssh command line user.  Can this be done?  If so how?

Thanks in advance

Jim Gilpatrick