Yes they are ripping off Rock Band. Harmonix repackaging and selling an already established Japanese game with a third party peripheral maker (Red Octane) as their publisher for the orginal Guitar Hero doesn't change much other than it's possibly tradition amongst the sub-genre to keep one-upping each other with knock-offs.
I honestly don't care though. Whoever delivers the better Band game in the end wins my money. And if GH IV is the better game like you suggest (and I'm leaning that way myself) then so be it. I'm really not all that concerned about who did it first when it comes to entertainment, just who does it best.
No they are not. They are ripping off Konami's drum game (I forget the name but its been out a long time) and Singstar just like Rock Band is.