I think you can! I think the program has to specify on their program page somewhere about J1 visas and their specific policies. I would call programs you're unsure of. Good luck!
You can but you have to explain in a letter when are you going to be ECFMG certified and provide the dates you scheduled your exams. But typically for an IMG everything has to be perfect, so most IMGs are already certified by the time they submit their application.
