When I first read this, I talked with the manager of the Home Depot (Canadian) in my area.
He said, "We supply uniforms and stipulate what may be attached to those uniforms, and it has nothing to do with religion......" This chap is Free Methodist and twice-born. He sure doesn't stop employees from reading scripture during lunch period.
The primary reason for the uniforms is store representation and customer service. They are readily identified. A political badge, for instance, would set the store apart from its purpose.
I can't speak for this one American store, or the American Home Depot. I do know that our Home Depots are the greatest service stores in our area. When wife shops there, one chap always rushes over to welcome her and help her find the little thing she is after. Love Home Depot.
Cheers,
Jim