I recommend to not use register_event/message when you can use register_logevent or something else instead. Why? Because last versions of AMX Mod X provide new emessage_* natives that may mess with other plugins. I already saw few plugins whose authors wasn't careful enough with emesasges_*. Some coders not quite understand when they should and when they shouldn't use that new message system. When you hook logmessages instead of messages/events you can be sure that no confilct will happen. And as for your last question: no.