Yes, they can.
I am a Computer Science & Engineering Graduate and find the syllabus for the Departmental Exams ( during training) pretty undaunting.
There are no prerequisites to getting selected to IAAS, or for that matter any other civil service, other than the standards set by the UPSC. You are taught whatever is needed for the performance of your duties after you get selected. In our entire batch, there is only one commerce graduate. There are 6 doctors, 2 economics graduates, a psychology student and an MBA.
The rest are all Engineers.