Yes, its possible. But it will be may be a little complicated in OLAP - depending on your cube design.

The way to get this to work, is to take your original OLAP hierarchy and show the 2 level attributes independently in the cube (they are already there, they just need to be set to "visible". A 2 minute exercise). Then, use the lower attribute to drive the page repeater; while using the upper attribute to drive the publication slices.

Using the a single hierarchy (with multiple levels) to drive both actions will probably not work.

Let us take a look and see what we can come up with. Do you have access to the yellow data modeling tools?

Douglas

There are 2 solutions. 

1. The first involves upgrading to 2020.15 - where we added a tweak to the page repeater engine that will allow you to cascade the selection using parameters and lists. Here, you would first create a parameters of the regions. Next, create the inner list of countries that is filtered using a "nonempty" filter and the region parameter. After that, add a region list slicer (you could reuse the region parameter again) as the publication slicer. Then create the page repeater with the country list as the slicer. When you wire up the region slicer into the country slicer, you will see the option to set its parameter. And that's it. the rest works.
2. Another technique, involves you creating your own data model with 2 columns in it: regions and countries. To keep it easier for the next part, make sure the names are EXACTLY the same as the cube's regions and countries. Now use the regions in your own model to build the publication slicer. Use the countries in your own model to build your page repeater slicer. They will auto cascade. Last, use the model mapping to wire up the values in your own model to the cube's dimensions so that they interact properly. And that's it. the rest works.

#1 is better if you can get the upgrade. #2 is not a bad stop gap until you upgrade.