Just a quick question - if I select Prot as Loot specialization in Flex, can I get gear with haste on it? That's it basically.
No. If you want to see what loot is available for your chosen specialization, open your encounter journal (shift-J by default?), select a raid --> boss --> loot window. Set your loot filter to your class and then set it to your spec. Those are the items that you can win.