Is there any way we can use WordPress for part of our site (directory listing) and use the IPS authentication for all users?

Any ideas or experience sharing is welcome.

Take a look at:

 

As mentioned by Randy, you could use a wordpress login method to do this from wordpress. This would allow you to use the IPS platform as the login method. Bear in mind however that it would not automatically have you logged into the community when you log into the wordpress side and vice versa. For that, you would need a full SSO solution