From my experience in the military, the only way they would do so is if they are going to be deployed or specifically working with that type of unit in the field. That way they are familiar with each other, otherwise I've never heard of anyone being able to train with other branches just for the training. Its best to refer up your chain of command if this is something you were looking into and wanted to take part in, your "higher ups" would be able to give you a definitive answer, find an answer, or, as the say, "hook you up" so you could.