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The short answer is that you can (see Dave DeLongs answer). The long answer is that you can't. Both are true. A better question might be "Why do you need to know?" In my opinion, if you can arrange things so that you don't need to know, you're probably going to be better off.
I'm not saying that you can't do it, or even that you shouldn't. What I am saying is that there are some hidden gotchas when you start down this path, and some times you're not really aware of what all the unstated assumptions are. Unfortunately, programming correctly depends on knowing all the little details. Off the top of my head, here's a few of the potential gotchas:
To the best of my knowledge the set of Core Foundation types has increased in each major OS release. Therefore each major OS release has a superset Core Foundation types of the previous releases, and likely a strict superset at that. This is "observed behavior", and not necessarily "guaranteed" behavior. The important thing to note is that "things can and do change", and all things being equal, the easier and simpler solutions tend not to take this in to account. It is generally considered poor programming style to code something that breaks in the future, regardless of the reason or justification.
Because of Toll-Free Bridging between Core Foundation and Foundation, just because a CFTypeRef = CFStringRef does not mean that a CFTypeRef ≡ CFStringRef, where = means "equal to" and ≡ means "identical to". There is a distinction, which may or may not be important depending on context. As a warning, this tends to be where the bugs roam freely.
For example, a CFMutableStringRef can be used where ever a CFStringRef can be used, or CFStringRef = CFMutableStringRef. However, you can not use a CFStringRef everywhere a CFMutableStringRef can be used