roller rockers means there are rollers on the rocker arm which depress the valves. having rollers on the rocker arms reduces friction on the cam and the rocker arms. this also reduce the rotating mass on the cams b/c the cams are smaller than the previous sr20s and which lets the engine rev easier.
The B13 SR20DE is different in the emissions stuff they have on it. The 91-94 cars have OBD1 stuff on them. The 95 and up cars have OBD2. As I have learned the ECUs have some differences in them too as far as what they can control--again the emissions crap. According to a thread David posted at another website, JWT told him to use a 1995 ECU to turbo our Sentras to control the engine and that we would probably lose a couple of minor smog control devices. I know that one of those devices involves evaporative missions. I also know that a guy on the SR20DE BB converted a 97 ECU for use in his 98 B14 in order to turbo it. If that is what is behind your question, I suggest you head on over to that website and drop him a line. Look under the turbo forum for signature Ben 98 turbo, or something like that.