Coming from my personal experience, I still lean towards no. I had a discussion with Nancy Hanson about this and we came the the conclusion that the CLA was not a destination, but the opening of doors to learn (yes, this was alluding to the CLA Summits). Personally, I had 0 experience using OOP when I got my CLA. But after my second CLA Summit, I found an application that deserved a very basic OOP architecture. The CLA Summit opened that door for me. Now I would say ~50% of what I do is OOP. There is still A LOT you can do effectively without OOP. And keep in mind that part of a CLA is to make architectures that your less experienced developers can use and understand. If they can't use OOP, then your OOP architectures will not be effective.
So should it be REQUIRED? No. Highly recommended? Absolutely.