Actually, with some nurses, they do. I have seen it and experienced it first hand. Now I've never been down-right disrespected or anything because of what uniform I was wearing, but the reception is different. When I walk in wearing my commercial service uniform they immediately listen aptly, assuming I know what I'm talking about. When I used to walk in wearing a volunteer uniform (although I was paid) they would not give such a warm and welcoming and listening reception until I started giving a report, then they realized I knew what I was talking about.
I don't face this anymore, now that I've been around long enough that most of the triage nurses at least know me by face, if not by name, no matter which uniform I'm in.