Programing other Atmel ARM chips using Arduino
Yes it is possible. IDE 1.5.+ support different platforms, as they call it. Where the AVR and sam are provided by stock. Others are possible. 

It is fairly involved setup. In short; within each platform there are the following files:


boards.txt, defines the individual boards using the similar processor.
platform.txt, defines the compiler arguments
programmers.txt, defines how to program it.


With corresponding sub directories to match, under the variants/ folder.
I have not found an complete tutorial on the matter. However, their 

Arduino IDE 1.5 3rd party Hardware specification

An overview of the platform architecture proposed for Arduino 1.5 

are a great place to start. 

I have not done much with SAM. I do notice that programmers.txt is empty. So it must be done another way.