That’s two different things. Never have your funds on an exchange, except for the part that you are trading with. Never ever use an exchange as a wallet, because in almost all cases you don’t have or can obtain the private key of the exchange address you’re using. Meaning, if they temporarily or permanently close, if they are being ddos-ed, hacked or otherwise robbed, run a ponzi scheme or on a fractional reserve, you’re in a bad place and have temporarily or permanently no access to your crypto. Mt Gox was a good lesson, but it’s still Wild West out there. Beware.
The address you are using to send your contribution from, is also used by Decorum to send the PDC to. If you would use an exchange address for sending Maid or Bitcoin, it would not show the PDC after it has arrived. Then you are in a bad place again, if the exchange cannot or will not help you recover the PDC. With Omniwallet it has best of both world: You own the private keys of all addresses in the wallet, you can check the arrival of PDC immediately, and have full control over the funds in your wallet.
Remember to have a little Bitcoin in the Omniwallet too, for miner fees and transaction costs while doing a non-Bitcoin Send transaction.
Hope this helps? 