ORIGINAL: Bebop Cola
If you look at the race files, there are separate spawn chance percentages for each type of character. As such, I would assume each Academy just modifies the spawn chance of their respective character type from the base specified in the race file.
This and logic suggests it would stack.It would be nice to know how much each building improves spawn rates.
The human scientist spawn rate is 1.15
random character appearance chance: Minimum=0, Normal=1.0, Maximum=3.0