sure. you can easily load external java libraries and integrate Talend jobs inside of existing programs. Talend is probably the most flexible ETL tool on the market-- as long as you have some good people to power it. Java developers do particularly well, especially if they have DB background. The components you would use to integrate with an external api would be any of the custom code components, tJavaFlex, tLibraryLoad are the first to come to mind.
use a tLibraryLoad component to import your API jar file(s) Then simply call them with some code. How you integrate with the API depends on what you are doing with it. If you are calling the API for every row of your data, then making the calls in a tMap might be a good idea-- if you are simply setting up some environment or reporting the results of a job, a simple tJava would be best. You can get examples on usage from every component by putting it on your canvas and pressing "f1" each component should be fully documented and have a use-case example.
I'm now successfully making the API calls and data is being returned. The issue now is that the data is all returning in one object bean and i cant seem to figure out how to separate the fields to create an XML file.