Your question makes me realize I have a fundamental misunderstanding about Xfbdev usage. I actually have both Xorg-7.7 and Xfbdev. Using a bootable USB flash drive, I started with Xorg on a Dell notebook and got it stable. I then worked and worked to get the MacBook Pro running but had no luck until I added the Xfbdev, and then only if it was loaded after Xorg, so I've left them together in the onboot.lst. It got that way organically and didn't cause any issues on the Dell.
I will go off into the forum posts and try to learn more about Xfbdev theory, and try your troubleshooting ideas of separating the two. Do I still load all of the Xorg deps separately?
Back to my original Mac track pad issue with Synaptics synclient not running, I found that if I load in this order 'Xfbdev Xorg-7.7' then synclient works (but the MacBook Pro won't start X, it will boot to text). However, if I load in this order 'Xorg-7.7 Xfbdev' then that breaks synclient (but the MacBook Pro starts X beautifully). At this point, I think my alternative is to build a 60-synaptics.conf to hold my preferred touch pad settings.