As far as I know they develop and maintain their own operating systems.
They have the procurve (provision) software, wich run on the original line of HP switches, and the Comware OS, version 5 and 7 on the H3C switches (orginal 3COM switches).
The Comware series is more advanced that the procurve series. (correct me if Im wrong).
Yeah the A-series (comware) are the more advanced compared to E-series (procurve/provision).
As the story goes Huawei stole (or somehow "found") the source code for Cisco IOS and used that in their first deployments. This (forked) codebase was later the one used when Huawei teamed up with 3COM and created H3C who later was aquired by HP.
Nowadays I doubt there are that many Cisco IOS left in this current codebase - the funny thing is that many of the bugs early Huawei equipment had was exactly the same as the ones found in Cisco IOS (including backdoors was the same). Also NSA hacked Huawei not too long ago so I guess they are even by now ;-)
Worth noting HP A-series is used by the US Army among other US Government branches which is why you will see a "US" version of firmwares when you go to the download pages (on the other hand given the snowden docs I dunno if its that sane to use these US-versions or not).
