it should work (the hacmp support matrix (http://www-03.ibm.com/support/techdocs/atsmastr.nsf/WebIndex/TD101347) does not care about TL max levels, only about min levels of your OS) BUT you...
Not official and so not sure if this is sufficient for you but we have did the same upgrade like you want to do and there is one box that has HACMP 5.3.0.4 and we did not update HACMP.
Our support...