I have a POSB savings acc & DBS multiplier acc. My CDP account is linked to my POSB acc. If my dividends payout is credited to that this acc, will it unlock the Multiplier investment category?

Yes but you must remember that int is paid only based on the money in multiplier

Yes it'll. Tried and proven. The good thing about multiplier is that the conditions can be met thru different accounts.

However do note that the additional interest is only paid on the multiplier account itself thus i put all my money there to get the extra interest. (E.g. Transfering the dividends from POSB to Multiplier as soon as its credited)