Stans sealant doesn’t state that it contains Ammonia, unless it’s added as part of the other 1% trace bits so there would be very little in the slop added to a tyre
Materials Saftey Data Sheet for Stans
Regardless, ammonia dissolved in water does not corrode aluminium unless you go to temperatures above 500 degrees Celsius, or it it has a high copper content (6061 Aluminium alloy commonly used in the bike industry has a low copper content), and even then, the corrosion only penetrates micrometers into the alloy.
(Disclaimer: This dredged from the depths of my mind from a 16 week of materials science course from 1998, my memory my be playing me up again)