Yes, you can veiw them "online" with either an ftp client. an ssh client, telnet, or a browser that is capable of using ftp (most are).
Understand, however, that they will not be "served" by a web server as there is no instance of Apache set up yet for that space if you have not yet "added a domain" to your hosting plan.
In any of these instances, you will need your user name and password to view the contents of your space. To view in a browser, the url is:
where "foo" is the name of your assigned server (the same you used to ftp the files there initially). When browsing to that space, you will be asked for your user name and password.
If you would rather make these files publicly available, and accessible via an http request from a browser, but do not wish to register a domain, Dreamhost will let you use a "dreamhosters.com" sub-domain for free
To do this, just go the the Control Panel-->Manage Domains screen and select "Add a domain /sub-Domain" link at the bottom of the page. Input "something.dreamhosters.com" as the name of the domain ("something" can't be whatever you want as long as it follows domain naming rules, and it isn't already in use by another or reserved by Dreamhost) select the other options , and submit the form. Once the setup is completed, and the DNS has updated, you can then visit that space with a url of http://something.dreamhosters.com.
By default, DH will put a directory (folder) in your space called "something.dreamhosters.com", and that is where you should place files you want to be accessible with that urll. Good Luck!