I believe it is, altough I haven't tried myself: about an year ago I was shown a Google Docs integration with OpenERp/Odoo, using web services.

The trick was to use the "admin" user.

You login with a cloud user and password, but behind the scenes, in your Odoo instance you are using "admin". You have to set a password for "admin"; this password will then be the one to use for the web services (and it's not the same as the password for your cloud login).

Thanks for your answer, I didn't see https://openerp.my.openerp.com/forum/Help-1/question/Is-the-Xml-RPC-API-available-on-OpenERP-Online-915

I was able to state a poc with curl thanks to this post:

curl --data '<?xml version="1.0" encoding="UTF-8"?>
<methodCall xmlns:ex="http://ws.apache.org/xmlrpc/namespaces/extensions">
    <methodName>login</methodName>
    <params>
        <param>
            <value>podbox</value>
        </param>
        <param>
            <value>admin</value>
        </param>
        <param>
            <value>admin</value>
        </param>
    </params>
</methodCall>' https://podbox.odoo.com/xmlrpc/common

<?xml version='1.0'?>
<methodResponse>
<params>
<param>
<value><int>1</int></value>
</param>
</params>
</methodResponse>