I was just wondering if boss rush can be an added category as well for the disney afternoon collection.

There is a separate leaderboard for The Disney Afternoon Collection: https://www.speedrun.com/the_disney_afternoon_collection
It includes Chip 'n' Dale, Chip 'n' Dale 2, Ducktales, Ducktales 2, Darkwing Duck, and Talespin. All include the Any% and Boss Rush categories.