The outdoor range I used to RSO at had little buckets that people could dump their brass in (most let it fall to the concrete shooting area floor). People, including myself, could root through the little buckets to extract the brass they wanted.
We'd even sort out popular calibers, and have a ".30-06 Only" bucket, a ".30-30 Only" bucket, and so on.
Some of the guys were regular "action shooting" types, and would bring a pair of gloves and a respirator and root through the 55 gallon drums of brass we had waiting for the scrap guys to pick up (all the money went back to the county, as the range was run by the sheriff's department and open to the public, so we didn't lose any money).
It was considered polite to ask if others were going to keep their brass after shooting before starting to collect it. I'd do that, and if people were shooting calibers I loaded for and said "no, I'm not going to keep it", I would politely ask if they could save it for me for when they leave, but mention that if they simply left it where it was, I'd be more than happy to pick it up for them. Most people would give me a little pile of brass on the shooting bench, so I was happy.
I reload, and I encourage others to reload. Most shooters don't, and picking up range brass at ranges that don't mind it is a cheap way of getting brass for reloading. I have no problems at all with it, as long as people are polite. Lurking about isn't impolite, but picking up your brass without asking is not terribly nice.