You can adjust the tuning of the backing tracks from the standard A4 = 440 to values between 415-466Hz.
Within iReal Pro:
Android, tap on the Settings icon (More screen in older versions of iReal Pro) at the top of the main library page and scroll down to Tuning to change it
iOS, tap on Settings icon (More screen in older versions of iReal Pro) at the top of the main library page and scroll down to Tuning to change it