I did get a direct reply from Jeff Petersen at RME (Synthax). He indicated that because of bandwidth issues the FF800 "sometimes" doesn't play well with other drives on a hub. He suggested cutting down on the bandwidth in the settings app for the FF800. I've tried that and it didn't help. He suggested trying the FF800 alone on the hub. It didn't work (I tried both bus and self-powered modes). I use a MacBook Pro and have attempted to run the FF800 off the Firewire 800 port while running firewire 400 drives off the other port. Not sure whether it was the Mac or the 800 but when I tried to use both the Firewire 800 port didn't work.
I have none of these problems with my Fireface400.
At this point I've pretty much concluded that there isn't any way to use the FF800 on a hub. I don't think I've ever encountered with with Firewire. It seems that the best you can do is to connect a firewire drive with 2 ports in the middle of the chain and put the FF800 at the end (I haven't tried chaining multiple drives) The other alternative is to do what I've done and that's to start using USB2 drives on a USB hub and leave the FF800 alone on its own bus.
If anyone has discovered a model/make of firewire hub that does work or a workaround I'd sure be happy to hear about it.