Unlikely. iOS7 and 10.9 use TextKit which wraps CoreText and in turn they have dramatically enhanced CoreText in the process. The code is unlikely to be compatible. It will likely require a patch for the older code.
Security relevant crash bugs are normally back ported. In any case, TextKit is just a wrapper of CoreText (like you said) for easier use within AppKit/UIKit — all the text handling is still done by CoreText.
