Ok, so I verified the device is recognized by Knoppix 5.3.1, which uses an older kernel, slightly, than Slackware 12.1. According to Knoppix, it seems to be recognized with the sl811-hcd module.
Oddly enough, I found this compiled in
and manually loaded sl811-hcd.ko and sl811_cs.ko with insmod.
For good measure I then did udevadm control --reload_rules
Still nothing, but the thing finally showed up when I turned the power of the external drive on and off. (which hadn't worked before)
Well, then it was the same as any other hotplug event, with the partitions recognized as /dev/sda1 and /dev/sda2 and with lsusb showing:
Bus 003 Device 004: ID 04fc:0c25 Sunplus Technology Co., Ltd
Guess I'll try adding those modules to my initrd and see if the thing is recognized at boot.
Since I only know half of what the heck I'm doing, any input/comments would be helpful. If not, hope this helps someone else out.
[Edit SOLVED] all I needed to do was add sl811-hcd.ko to my initrd.