Pretty sure all the coins on Polo or any exchange would be valid for the new distribution.
But some clarification on all that would be good.
I hope so, because anything else would be a ripoff!
Lets say we both have 50k Clams on Poloniex it may happen that we get different amounts of Doogcoin depending on which coin of ours was deposited after and which one before block 730000.
And the funny thing is, we have no control about it whatsoever.
If you deposited your coins after block 730k, then you would have newcoins in your local wallet (since that's where they were as of block 730k).
If you deposited your coins before block 730k, then your newcoins would be in Poloniex's wallet (since that's where they were as of block 730k).