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.
Ummm, I wouldn't install it on a computer that you want to use for general computer usage. As a general rule, I advise people to wait until at least the .1 release, if not the .2 release for each new version. So using the beta is definitely a no-no, unless you actually need the beta, for testing your application against.
Otherwise you can find pretty big things not working - printing, might not work on one release, or bluetooth preferences might not open on another, or Airplay video streaming might not work. You may have graphics glitches, or a run away process that kills battery life. It's simply not worth the pain if you don\t really need it, but if you do really need it, the pain is bareable if you grit your teeth.
Though it's only a matter of time before somebody posts it here as a comment.