I am able to enter and I own "Dead Island Definitive Collection" which says in the features "Includes all previously released DLC!" and I wonder if this is one of the DLCs that includes with "Definitive Collection"

Edit: Okay, while I was searching discussions page, I have come across a message from 2020, a user shared one of his "Dead Island Riptide - Fashion Victim DLC" key and I have tried to activate it and Steam gave a warning as "Product Already Owned".

So, yes, "Dead Island Definitive Collection" have the "Fashion Victim" DLC.

Edit 2: Now I am not sure, I have found that I also own the old "Dead Island Riptide" along with "Definitive Edition" and I had Fashion Victim DLC owned under the "Dead Island Riptide" so, I am not sure.

Everyone can check here if you don't own it Steam DB link

thks