I can chime in on this one. I have been running a wet/dry sump on my tanks for 2 years with no issues.
You do not want to use two pumps to run these systems as it is WAY too hard to synchronize the pumps and prevent the sump or the tank from over flowing. You need to use a siphon to pull water from the DT into your sump and use a pump to return the water to the DT. Since mine is already set up and in use it's nearly impossible to get pictures of the system in use, but I dug up some pics from the original build.
I have a 75g DT with a 20g sump. I'm using a hydroponic medium for my biological medium and have hed no problems with it at all. Once every 2-3 months you just have to stir it up really good.
Here are a few pics. I apologize for the bad angles, but, like I said, this is an operating system that is quite inaccessible.
This is the siphon when it was originally built for a 20g:
This is the wet/dry sump
This is the siphon drain coming off of the DT.
This is the stand pipe inside the DT.