This question can be approached from two perspectives:
- is your task to create automated tests, or
- is your task to automate content creation?
If the former, there is a number of tools (both commercial and open source) which can automate test scenarios on web-based applications. Oracle has one too, called Oracle Application Testing Suite.
If the latter, there might be better means than generic testing tools. Take a look at this article: http://manifesto.co.uk/using-webcenter-sites-rest-api-part-1/?goback=.gde_142076_member_5809268750695821313#!
which describes REST API. Also, if you use WebCenter Content as you content repository, you could use Batch Loader, or RIDC interface.
This very much depend on what you mean by 'effective'?
With Proxy asset types you don't need migrate the content - you can leave it where it is and integrate with the 3rd party repository (Proxy Assets: Integrating Third-Party Content Sources - 11g Release 1 (18.104.22.168.0)) Without having personal experience I guess that accessing or retrieving content in the external repository will be slightly slower, but on the other hand you will spare time necessary for content migration and also maintenance tasks (such as backup) will be different.