I have before. I used to use the K&H Run and Gun 200 vest. Great vest... just not backpack for a decoy.
I mainly used the backpack whenever I wanted to lug around a decoy, some extra water and food. Also would keep a rain poncho in there and an umbrella that attaches to a tree.
I would bring that if I knew it was gonna rain later in the day.
With that said... I know have the grand slam vest that has a nice game bag in the back. Gonna keep a Montana Jake decoy back there.
Probably gonna keep the backpack in the truck with the extras if I need it.