Income tax returns can be filled by anyone, even a salary person or one who is earning from interest. (it depends on the skill of the filler)
usually CAs and TRPs are doing this work bcoz they are highly certified and trainned in manner to help those who are unaware of Income Tax Act and its sections.
This can be depends on the agreements between the employer and the employee CA, usually they dont allow or you can say he dont get time out of service.
anyone can file it return. There is no prescribed qualification or condition given in IT ACT. even u can file d return being student or assesse himself find d return.
for second question yesss he can provided terms of employment does not prohibit him to work in his personal capacity mostly many people work in july n sept to get some extra money. no one can know this
ANY ONE CAN FILE RETURN OF INCOME OF PERSONAL AND OTHERS, THERE IS NO BINDING AS PER INCOME TAX ACT, BUT SIGNATURE ON THE RETURN CONDUCTED BY THE PERSON WHO IS LIABLE FOR FILE THE RETURN OF INCOME.
Where the data of the Return of Income/Fringe Benefits in Form ITR-1, ITR-2, ITR-3, ITR-4, ITR-5, ITR-6 & ITR-8 transmitted electronically without digital signature