Short Answer: yes, MCAs have known to do MBA from the IIMs.
Long Answer: Sda is spot on when he says you don't need a past precedence to actually justify your need for an MBA. The way I look at it is that a MCA is just a 6year route to get where a 4yr Engineering degree might get you. But along the road you pick up a lot of invaluable non-technical experience.
Arun
PS: I know for a fact because I am an MCA myself