Originally Posted by
Covidian98
This question is more about being able to use the frequent flyer benefits of each airline, in a mixed airline itinerary, and not so much about crediting the points or miles to one of the programs.
Yes you can typically use the credit card benefits whether or not you credit the points to the program. As I posted above, just pull out your credit card if you need to (you may want to show it to the gate agent before boarding to make things smoother).
I believe in the case of reserving Economy Plus, those segments must be credited to Mileage Plus, so follow
canadiancow 's advice on that.