Unfortunately, the Arduino SDK we published uses a pre-compiled library, mainly because of internal project structuring that made it difficult to separate out proprietary code in the time we had available. The library is currently only compiled for the ATmega 328p, and is thus only compatible with 328p-based Arduino boards such as the Uno or Nano.
Due to memory limitations of the 328p, there also isn’t enough space to support the full RVR command set. For the time being at least, Raspberry Pi is the best embedded platform to use with RVR since it supports all of the new firmware features that we released in the August firmware update. For basic features, an Uno or Nano can work well, or a micro:bit.
Also note that many non-Uno Arduino boards use USB-serial ICs that require special drivers and aren’t yet supported in RVR’s USB stack, so you’ll need to connect to the UART pins on the RVR expansion port and use level shifting if your GPIO pins aren’t operating at 3.3V.
Happy programming, and sorry again about the disappointment with the 2560.