Do they have the same sysex identifier IE 0x70
it simply a 7 bit with 3 bits zeroed and if so which bits ? The first or the last ?
It is – the data uses the 4 ls bits. Se the "Sending Key Presses via MIDI" document on the H8000 support page for examples.
The SYSEX_SCREEN_DUMP is for experts only. You should not even consider using it if you don't have an H8000 to get test messages.
Is it possible to communicate with the H8000 via Ethernet or is midi the only/by far the simplest solution ?
No Ethernet. MIDI is probably best for you as Eve/Net is a proprietary non-standard protocol.
Does the EVE/NET controller get it's screen data via midi ?
No. It uses Eve/net which runs at up to 1MB/sec