Wordpress integration is unofficial so it's impossible to say without knowing where the you're using came from, but if it was written properly you should be fine to replace your current copy of the chat folder with the one from 0.8.8 EXCEPT for the following files:
- lib/custom.php
- lib/config.php
- lib/class/CustomAJAXChat.php
- lib/class/CustomAJAXChatInterface.php
- lib/class/CustomAJAXChatShoutBox.php
Like kadu said, back up your existing folder and try it out. It's harmless, as long as you keep your original folder in case of a problem.