It is possible, but not as straight-forward as adding fields from a table. Also, be aware that Catalog Tasks have different variables, depending on which Catalog Item they are associated with, so adding a few variables from one Catalog Item will show blank in all of the other Catalog Task records. Variables show their true value, so reference and list collectors will show sysids.
https://www.servicenow.com/community/now-platform-forum/catalog-item-variables-on-ritm-list-view/m-p...
