Seems you have 2 questions:
1. Will image clean up & catalog backup run at a same time?
2. Can image clean up & catalog backup run at a same time?
Question 1 may be asking if NBU will automatically run the two at the same time.
My experience has been that NBU automatically runs image cleanup after catalog backup has completed.
Question 2 seems to indicate that you want to run both at the same time.
So - which one is your actual question?