Sure you can.
Be aware of the fact that ONLY the FE model will be transfered (geometry is "virtual" inside Workbench, once you link to a geo file coming from a CAD), together with the Named Selections (which, in Classical, are the "Components").
Vice-versa, you can also read back in Workbench results generated with Classical, PROVIDED THAT the Workbench's ambient has the same exact geometry memorized and the exact same mesh.
For example, it will not be possible to interprete a RST file ALONE in Workbench coming from a model entirely created and solved in Classical. However, the following "mixed strategy" works very well:
build model with CAD -> transfer to Workbench -> mesh in workbench -> setup a loadcase in Workbench -> write input file for Classical -> read it into Classical -> manage the solution inside Classical -> read the rst file from Workbench and post-process inside Workbench.
Regards