UCD9090-Q1: Question regarding GPIO Configured as Open-Drains

I am using UCD9090-Q1 (and UCD90160A), supplied with 3.3V. If I configure a GPIO as open-drain output to interface with 1.8V logic, can I pull this GPIO up to 1.8V? Reason I am asking, is I wonder whether a GPIO's input circuitry is still active when it is configured as open-drain output, in which case it would not want to see any voltage between logic states. (See http://www.ti.com/lit/an/scla015b/scla015b.pdf)

Please let me know if it's safe to do so.
Thank you.