Is there an API that exists that would allow me to convert Solidworks/Catia files in bulk?

Since there isn't a way to do this now, it's not likely there is a software interface to it.

You can try the Unite technology that does on-the-fly non-parametric conversion. New Release: Directly Open SolidWorks, CATIA, and NX in Creo | PTC

CrossManager can convert CATIA and SOLIDWORKS files to neutral formats such as STEP or IGES in bulk.

It can't write native ProE files, but maybe neutral formats can suits your needs.