I don't have an 8000 here to try this, but I was syncing a Novation Supernova II to Logic earlier this week, so I'll give it a shot.
The basic part is, you need to set the 8000 to external clock mode, and tell Logic to transmit MIDI clock on the output port where the 8000 is sitting. Assuming you're doing that correctly, it's hard to see what you're doing wrong. Perhaps you could give us a few more clues about the nature of the problem.
If you're having trouble setting the gear up, the owner's manual is your friend. In Logic 4.5 on the Mac, MIDI clock transmission is under Options -> Settings -> Synchronization Settings. In the dialog box, choose the MIDI tab. The click the check box and choose the output port.
Recording the arpeggio into Logic is not necessarily a bad idea. If you do this, it's a lot easier to get the arpeggio pattern to have a reliable relationship to your bar lines.
You may or may not encounter goofy MIDI loopback issues, in which the 8000 transmits arpeggiated notes to Logic and then tries to re-arpeggiate them when it sees them returning to its MIDI input. But that isn't the problem you're describing.
Pim's tip about delay times is correct, but as well as I can recall, Roland's delay times tend to be set in 10ms increments at best.
Good luck!
--Jim Aikin