I sent Bittrex a support ticket asking about making Gas available to NEO holders in Bittrex and this is the reply they sent me this morning:
This reply is intended for all people who have traded and withdrawn NEO and have raised questions/concerns around lost coins on withdrawals, the withdrawal fee, and neo gas.
We have blocked the withdrawal of anything other than whole numbers. This should stop any truncated NEOs. If you get an error, make sure that the "Withdrawal" box on the bottom of the withdrawals dialog is a whole number.
All funds not sent due to truncation on NEO withdrawals have been refunded. Once we fixed the whole number issue it was easy for us to calculate that and refund it back. These will show up as deposits in your deposit history.
We've lowered the tx fee to 0.025 and will adjust accordingly with the price.
Lastly, we are still working with the devs to see if we can distribute GAS, but it is not a trivial matter. Whatever we decide to do, it will be going forward only. We will not retroactively credit GAS to anyone since we have no records to do so. At this time it is still recommended that you hold your NEO in your own personal wallet if you would like to collect GAS.