The J9575A - here actual QuickSpecs - is now called (branded) Aruba 3800 24G 2SFP+.
Before the Aruba acquisition by HP the J9575A was called HP 3800 24G 2SFP+, since HPE was created it then became HPE 3800 24G 2SFP+, now it's Aruba.
The JL071A - here actual QuickSpecs - as yet written above, is a completely new Switch called Aruba 3810M 24G 1-slot.
They both uses ProVision software (now called/renamed ArubaOS-Switch) but the J9575A uses the KA branch while the JL071A uses the KB branch which is the same Software branch used by the 5400R zl2 Switch Series.
This somewhat answers to your second question.
About Hardware, for sure there are differences: as example, the JL071A supports 40G links on QSFP+ Transceivers and, if I'm not wrong, I've also read that at Aruba there is a plan to support VSF (Virtual Switching Framework) on Aruba 3810 Switch Series during 2017 (read here).
It seems that Stacking Modules use different product codes (see QuickSpecs):
They look comsetically different but who really knows if this is the only difference. Maybe they share the same Hardware and there are only cosmetic differences.
I don't know if the Switch Software (KA/KB), once deployed in its Switch model, is able to lock modules down by doing a sort of Hardware blacklisting or just doing the contrary enabling them by doing a sort of Hardware whitelisting (The match, if any, can be done against hardcoded Modules P/N list, for any type of Switch series)...but, about that, I'm just speculating.
Stacking Cables look exactly the same (notice the name with reference to Aruba 3800/3810 series) so they are interoperables:
- Aruba 3800/3810M 0.5m Stacking Cable (J9578A)
- Aruba 3800/3810M 1m Stacking Cable (J9665A)
- Aruba 3800/3810M 3m Stacking Cable (J9579A)