We are looking to use rollup categories to group some of our items into different product mix groups. Does the Square API allow us to pull these rollup groupings?
Are you referring to categorizing categories within the Catalog? 
We have a bunch of items and item categories that when grouped in a specific way creates a “product mix”. My team let me know that this is doable, but we’re not sure if the API lets us pull that rolled up grouping.
Oh, this is the bundling of catalog objects. At this time the ability to do this with our API isn’t currently available.