There's no need to simulate the hotkeys, just run irotate from your ahk script using ahk's run command.
From irotate.htm:
Using iRotate command-line parameters
In addition to selecting iRotate commands from the menu, the program supports command-line parameters that allow you to call iRotate functions on start-up and from elsewhere in Windows at any time.
In the absence of special command-line parameters, when iRotate is started it normally checks your current display settings and then simply resides in the Windows system tray awaiting user interaction. However, the program will also process certain command-line parameters you may choose to pass it, either when iRotate is first started or while the program is already running. This feature allows parents and administrators to change screen orientation for specific users on startup, and allows you to create shortcuts anywhere (on the Windows desktop or in the Start menu, for example) that call specific iRotate functions.
iRotate is normally started with the command iRotate.exe. To pass command-line parameters to the program, you might add, for example, "/rotate=90" to the command-line, as follows:
Rotating the display:
iRotate.exe /rotate=90
where 90 is new screen orientation; other values are 0, 180 and 270.
Manipulating a specific monitor (multi-monitor):
iRotate.exe /3:rotate=90
where “rotate=90” indicates the screen should be rotated 90 degress. 3, the very first number followed by a colon, tells iRotate to apply these settings to the third monitor in a multi-monitor environment. Again: if a monitor is not specified, the display settings are applied to the primary monitor.
Non-resident changes:
iRotate.exe /rotate=270 /exit
Normally when iRotate is run, it resides in the Windows system tray. However, it can also be passed a desired screen orientation and instructed to exit immediately after applying changes. If you never want iRotate to appear and stay resident on the system tray, append an /exit parameter.