I don't know what capabilities the Documentum FTP Integrator has, but for Alfresco WCM the easiest way to get content loaded is to use either FTP (preferred) or CIFS to copy content directly into a user sandbox, then promote it directly to the staging sandbox (ie. without a workflow configured).
In Alfresco versions prior to 2.1.2, you'll need to break the content up into batches of less than 5,000 or so items, and load and promote each batch sepatately. This limitation has been mostly addressed in 2.1.2 and beyond, although I still tend to err on the side of caution and batch load content into the system in chunks of 10,000 items or less, while also trying to keep the total file size of each batch reasonable (eg. if I have a 10MB file somewhere in the source content set, I'll load and promote it separately in its own batch).
If you're managing structured content in Alfresco (ie. XML files backed by Web Forms) you'll probably also want to transform the source content into the XML format defined by your content model (XML Schemas) - this is left as an exercise for the reader (Alfresco currently doesn't include generic ETL functionality, and is unlikely to add it any time soon, if at all).
Cheers,
Peter
