My question is, can custodian wallet not be able to accept such dust amount?
If the amount of bitcoin you send is larger than the dust limit, nodes will accept your transaction and it doesn't matter whether the receiving address belongs to a custpdial service or a non-custodial wallet, but exchanges can have their own minimum deposit limit and it's possible that the exchange don't credit your deposit due to the amount being lower than their deposit limit while they have received the fund.