David, welcome to the forum! This is a great place to learn and to share.
Certainly the raw milk will have its own flora in it, and those flora will include the desirable bacteria that is used to make cheese. The problem is that you can't be sure that the desirable bacteria will be the ones that dominate, so you may or may not get a cheese that tastes good. Thus, even for raw milk, you should add culture(s) -- this will not eliminate all of the other flora in the raw milk, and that is good, as they will add depth to the flavor -- but it will ensure that the desired bacteria dominate.