Most of them are "cross-platform" I guess you could say. I find that it's not universally true, however. There was one broker called broker_unhittable that I liked during Cata. Did a breakdown of CTC caps and was really nice info to have. However, I know it worked with Titanpanel and did not work with Fubar. I didn't know about Chocolatebar then so I'm not sure if it worked with that.
Just wanted to mention a specific example I was aware of where they weren't universally compatible.
Also, there are some addons created to "port" a broker from one bar to another. Can't remember if it converted fubar brokers to titan or the other way around but I've seen at least one addon for that purpose.