To be honest, I have no clue, what your problem is actually caused by, so what follows are just some thoughts that may help you to track your problem further down.
If I read this thread correctly your problem occurs only on a system upgraded from Slackware 12.0 to 12.2, but not on a fresh 12.2 installation. This strongly indicates that it is not something inherently wrong with Slackware 12.2, but something that went wrong during the upgrade.
Here are my ideas, hoping they may point you to something useful.
1. It is usually not necessary to compile a kernel for USB device support. Only in rare occasions you need additional driver support for a particular device. But if the huge-smp kernel supports your device, in almost every case the additional driver will work just fine as a module with the generic-smp kernel (or the other stock kernels). Therefore my first suggestion is that you go back to the generic-smp kernel. Hardware support compiled into the kernel may interfere with the UDEV subsystem (not very likely, though).
2. When I upgraded from 12.1 to 12.2 on an old laptop, I overlooked the hint that the UDEV configuration had changed. As a consequence I lost support for my WLAN PC Card. I got it working again by removing and re-installing everything UDEV related, but at the cost that now I had no sound. The reason was, that somehow the firmware for my soundchip was gone, for some reason. Copying the Yamaha files from /usr/src/linux/firmware from another Slackware 12.2 system over to the laptop solved the problem.
May be you have a similar problem.
3. You might try to connect your camera with your computer using Digikam. If Digikam sees your camera, but you still can't mount it, this would, IMHO, indicate, that there is a problem with the USB device mode (PTP vs. mass storage).
4. To get it all straight, I would suggest the following steps:
- go back to stock kernel (generic-smp)
- remove UDEV and related packages, reboot, re-install UDEV and related packages
- install Digikam, eg. using a script from SlackBuilds.org or a pre-compiled binary from Slacky.eu or LinuxPackages.net (all of them work, as far as I can tell); see 3. above
- compare the content of /usr/src/linux/firmware on your working fresh 12.2 install with that on the upgraded system, do the same for any directories containing camera drivers
- compare the settings in /etc/modprobe.d/... and so on, to see if there is a module activated on one system that is blacklisted or commented out on the other one
Copy over all things you need for your daily work to your fresh 12.2 system, such as email, then do a fresh install on the upgraded system, too. It depends on the amount of data and configuration work necessary, which approach is more econonmic for you...
If nothing of the above solves your problem, it should at least help you to track the problem further down. The experts here will have a better chance to support you, then (and will certainly happily do so, as they helped me so often demonstrating A LOT of patience; so come back when you have a little more details).