"friendly" can be used to describe places and things as well as people. Some dictionaries I've seen give "a friendly greeting" as examples, so I've compared greeting, place and person on Google NGram.
I'm guessing when people say "a friendly place" they implicitly mean a safe environment where they wouldn't feel anything threatening or disreputable occurring, eg., outbreak of violence, shady activity, eg., drug dealing, street-walking etc. In other words, somewhere you wouldn't hesitate to take your kids along to.
I definitely wouldn't use "friendly" to describe a rough neighborhood, and probably not for some dive bar, just generally speaking because of the clientele that patronize it. Even if I think my neighbors are great people or know some great people who frequent a bar, I still couldn't make myself call either "friendly" places if they are generally speaking rough places.
"Maybe I'll go in here. It seems friendly enough."
Note: As an afterthought I wondered whether certain places can be rife with illegal activity, say the ones I mentioned above, and still be a friendly environment. I suppose it can. By "rough" I'm unsure whether you just mean in terms of violence, of in terms of what most would consider disreputable activity, ie., illegal gambling, illicit drug consumption and dealing etc. I'm not sure whether you count these things under the umbrella term "rough". Some of these activities could be seen as leading to a higher likelihood of violence, and any place where violence is likely to occur isn't a friendly place in my opinion.