The anatomy you will be tested on in EMT school will be a breeze. Nothing much beyond the material learned in a high school course. You won't learn real anatomy just with flash cards, so take a course.
I have used Gray's flash cards for college anatomy and physiology, I didn't use them as much as I thought I would but they are still a useful tool. I do really enjoy this clinical atlas of anatomy book I have, sorry but I don't have it with me to give you the title. I find that learning how things go wrong (ie: pathology) helps me make sense of how things are when they're right (basic A&P)