I know this is an outdated artical but I had the same question but i wasn't satisfied with the answer so I searched a little more into the matter and decided to post a replay for anyone else that is wondering the same thing. 🙂
http://www.wacom.com/en-us/comp
Wacom mentions that a device need to be "Bluetooth Smart" & according to ZDnet in 2015.
http://www.zdnet.com/article/apple-quietly-adds-bluetooth-4-2-to-iphone-6-iphone -6-plus-ipad-air-2/
Apple added it with a firmware update to 4.2. here's a quote from ZDnet worth mentioning.
The IoT aspect of the version is that it supports IPv6 for Bluetooth, allowing smart sensors to connect to the internet over the low-powered wireless standard 6LoWPAN.
As some reports suggest, it's possible that Apple has added Bluetooth 4.2 support via a firmware update. But despite Apple's updated specs sheet, it's uncertain whether support for the latest version of Bluetooth will translate into the benefits listed by Bluetooth SIG, since they may be dependent on new hardware.
Which sounds logical as you see on the official Bluetooth SIG
https://www.bluetooth.com/specifications/bluetooth-core-specification
The two most prevalent implementations of the specification are Bluetooth Basic Rate/Enhanced Data Rate (BR/EDR), which was adopted as version 2.0/2.1, and Bluetooth with low energy (LE), which was adopted as version 4.0/4.1/4.2. Each implementation has different use cases and each implementation uses a different chipset to meet essential hardware requirements. Dual-mode chipsets are also available for applications that include both use cases.
Bluetooth SIG mentions that each implementation uses a different chipset. Although Apple updated the firmware to 4.2 I didn't find news that suggest Apple updated the chipset (not to say they silently did so for newer manufacturing phones).
My only suggestion is try it. Get the stylist that meets your needs and give it a try - you can & should always be able to return it. 🙂