Zone 2, Exe and NEC are not related to each other... hence my safeguard on perhaps this being something related to UL certification.
I think perhaps you need to clarify better what it is that you are after.
The Remote IO or barrier will generally have two areas that it is intended for use. One is the physical location of the barrier, the other is where the instruments powered by such barrier go to.
So, a lot of barriers will be rated for ATEX Zone 0, but must either be in a safe area themselves or in a Zone 2.
Under ATEX, if you have more than a single intrinsically safe circuit going into a box, it then must conform to certain specifications. Exe rated type boxes are such a type of box and how most barriers or IO that can be mounted in Zone 2 is.
The field devices themselves may or may not require stringent protections if the protection concept is intrinsically safe... note that I said above more than a single circuit... most instruments will have only one circuit and if intrinsically safe they won't spark. However, most devices will be well protected.
Lastly, you should have some knowledge of the standard before installing these things. It's not that it's incredibly difficult, but there are little things to be aware of.