I can confirm here too that buying on Bittrex i'm able to see my holdings on the distribution graph.
If you have a look at the VTR rich list - the ~850k holder isn't in there:
http://[Suspicious link removed]/RichList/index.php?Currency=VTR
There is several explanations for this - but I'm assuming this just means Bittrex must spread out the VTR that they hold on the exchange across multiple wallet addresses for security reasons.
Correct. They keep internal ledgers of individual accounts. When that person removes all of their coins (if they do) then whatever address they send it too will have multiple inputs.
Whenever you deposit coins to Bittrex those coins are stored in your personal wallet address until someone withdraws the coins that you sell. They are not transferred to new wallets upon being traded. Only Bittrex's internal accounts are changed.