I don't know if there's a better way (if there is, somebody tell me) but you can ask the winner for a screenshot of the DLC store page when they are logged in ʕ•ᴥ•ʔ

Hello Darkchungee. You can view it by clicking on the winner's steam profile and clicking on "Games". Then type in the search bar "Borderlands 2: Headhunter 1: Bloody Harvest" and if they own it, it will show up.

Not all DLC shows up this way. Most of the time you will need to add someone to your friend's list to view it.