I have run both a Nikon 8000 and 9000 on the latest version of Leopard on a late-model MacPro (intel) tower with Nikon Scan 4.02. It works fine.
One thing you might check, if you are having issues, is whether you have ANY other firewire devices attached to the computer you have the Nikon scanner attached to. EVEN IF THEY ARE TURNED OFF it could be a problem.
In my case this manifested as the Nikon Scan software repeatedly failing to detect the attached and powered-up Nikon scanner. I have several external FW hard drives attached. Turning them off didn't do the trick; only detaching them completely solved the problem. I finally decided that having to disconnect my external drives every time I use Nikon Scan is too much trouble; so I figured out a kludgy way to attach the scanner to another older machine on my network, and control the software via Leopard's screen sharing capability. Only kicker is that I have the scanned files saved to the main workstation, so over a wireless network saving 500MB scanned film files takes a moment or two.
I've tried and tried to love VueScan, but duplicating Nikon Scan's ease-of-use with film strips of multiple images has eluded me. My Epson V-750 came with SilverFast and it's good software, but almost too much for my taste. So I'll stick with NikonScan until it's no longer supported, ie, likely the next version of OSX.