If you're using the wallet you posted about in another thread:
https://bitcointalk.org/index.php?topic=2699745.msg27594930#msg27594930 then you've got nothing to worry about. Encapsulated p2sh Segwit addresses (those that begin with "3") have no issues sending to and receiving from non-Segwit wallets.
GDAX's post should be about native segwit If you used Electrum native segwit, I believe you have no problems spending a segwit input to a non-segwit output... so yes, you could send GDAX bitcoin, but you wouldn't be able to receive it from them.
