I actually got denied on Delta because my ID didn't say Skyteam on it. A supervisor straightened that one out.
And yes, the uniform thing is sadly common.
EDIT: On the flip side we've been having a few guys try to jumpseat on us in shorts or cargo pants, sneakers and a tshirt. Also had a United pilot not actually check in (for a seat in the back) which is good because if we'd found out about her prior to getting to Maui we would have seen she was in a skirt and tanktop.
When I was at the last shop, who flew nothing but Delta passengers at the time, I had a gate agent give an AMR only pilot the JS about 40 minutes before the doors closed, and refused to give me the JS to get to work. Needed a Red Coat to straighten that issue out.
"You're supposed to be here an hour before."
"No, the jump seat is supposed to be released to someone OFL fifteen minutes prior"
"He was here first."
"Fly's American Passengers, I fly Delta passengers, I have priority. It goes Delta....etc."
"I already gave it to him, if a seat opens up (it was over sold, and they were buying people out), you'll get it."
"There are no open seats, I have priority. Call a Red Coat please."
"I don't have time for that. Go have a seat."
I ended up finding a red coat, and explaining to him what was going on. The gate door had already closed, but the hadn't closed the airplane door. Thankfully, the Red Coat knew what the issue was, and issued me a JS pass. I felt bad for the other guy, but he was headed to an event, and I was heading to work.