I wouldn't do this. Likely it will not cause any problems, but nothing will show up in the program. Even if you could get the tools to run, they have been updated for each version of the program (3, 4, and 5) as there were changes by Adobe that required changes be made in the actions that drive the tools. In other words, the tools will fail on one level or another when used in Elements 5 as they were not designed for it.
I am working on finishing up the tool set for Elements 5 this weekend. You'll be able to get it from my website (http://hiddenelements.com
) very soon.