I was an CIMB ex-mgmt trainee (back in 2002), but for their life insurance arm (not the bank itself).
Back then the bank was known as BCB, and their life insurance arm was known as Commerce Life.
I would say that these sort of programmes are excellent for fresh grads who intend to be in the financial industry, you get exposure to the entire operations of the company (via rotation) which otherwise will not be available to you if you were straight away hired as a permanent exec. So go for it!

You may or may not get into the department you want, but I am sure you will get into the 'suitable' department according to your qualifications, education background, & personality. A mismatch in these areas will be bad for you in the long run.
If you get into a dept you don't like, you can always ask for a transfer. You can always request, these things are negotiable. (especially if you are good at what you do)

Trainees are often judged by their interpersonal, communication, writing, & presentation skills. Behavioral assesment may also contribute. So, you will need to appear consistent in your efforts to catch the attention of the supervisor.
All the best to you!