The answer will depend on whether your agent machine's "agntd" process is running in multi-user mode or single-user mode.
If the agntd process on the agent machine is running in single-user mode, then only the userid of the user that started the agntd process has permission to connect.
If the agntd process on the agent machine is running in multi-user mode, then any valid userid and password (that would be able to login to the agent machine with "putty") can be used when connecting to the agent from Harvest.
You can tell which mode the agntd process is using with the "ps -ef | grep agntd" command. If the "root" user owns the agntd process, then it is running in multi-user mode. If another user owns the agntd process, then it is running in single-user mode.
After successfully connecting to the agent machine and logging in, the userid that Harvest is using must also have the appropriate permissions to read and write to the folder you want to use. Executing "ls -al /my/folder/name" will provide this information.
Let me know if this answers your question.