You cannot use Wordpress and IPB user database integration at the same time, you either use IPB users, or Wordpress users.
If you happen to use both Wordpress and IPB on the same site you could for example:
- Pick IPB for the user integration (choose IPB in integration mode during installation)
- Still use the Wordpress plugin to have the chat displayed in a Wordpress page with the [flasherize-chat] command as noted in the installation instructions.
It is really simple - you cannot use user integration from two different systems at the same time.