To some extent you can tell from their title and previous work, just like with developers. Foe example, I had an entirely non-technical boss that understood I might not be the guy to re-write some printer drivers because I was a web developer. He didn't know the specifics, but being in charge, knew he had to ask someone who did, or do enough research to figure it out.
Likewise, UI designers will specialize in designing UIs and be better at making buttons look like buttons than Graphic Designers, and Experience Designers will be better at integrating user feedback and research into projects. Just like you wouldn't trust any one developer to implement critical functionality you don't understand without outside input, you probably shouldn't rely on one designer to that either. If you maintain a project, though, you can't expect designers to instinctually work around what you don't know. Being in charge means that you're in charge of figuring out how to evaluate it. I'm positive that a "I'm not sure how to interface with this sort of thing. Let's work through it so I can figure it out." will be received kindly by people you should consider working with. Good design proposals should already come with explanation and justification to help you down the path
This is a random selection from a google image search of proposal ideas. It was from another post where I was talking about higher-level topics but the principle is the same. Changing a set of control widgets should require no less thought and explanation.
> Developers absolutely refer to developers with glib contempt.
ok— now copy and paste the rest of what I wrote. An overly opinionated, defensive person with veto powers that understands the purpose and value of your work is fundamentally different.
> solicited the wrong kind of designers
This points to me that the root problem is that we can't tell what kind is the wrong kind. It's a trust issue, but also a competence legibility issue.
That said-
> referred to developers and their work with the same glib contempt
Uh yeah? Developers absolutely refer to developers with glib contempt.