@Phillip - Mac support for this arduino support from simulink was added in R2013b... you can use this entry to initiate installation, but you will need 13b for Mac support.
I'm using 2012a for Mac OS x on 10.8 and when I type
targetinstaller, it pulls up the Target Installer window, but then when I select Internet as the option, I get:
"Select a Target
does not contain a valid support package. Please specify a folder that contains a valid support package and try again."
If I download the submission into my downloads folder and use the 'Folder' option and point it to the folder 'rtt_arduinomega2560_r2012a_v1_0' it also complains and says it is not a valid package.
Is there any plan of implementing this package for the Arduino Due? The Due is a much better platform and adding support for that would mean I can finally start using them with Simulink. Also, why don't you add some block for I2C and SPI communications. Most sensors and shields for the Arduinos use these serial protocols so this would go a long way in helping users make useful projects.