Yes, the iWitness can handle more cameras. I have used it for 9 cameras. My focus has been to capture snapshots when motion is detected. I find that the snapshot takes 4-6 seconds to activate using the SmartMacros. My other problem is that snapshots get saved with cryptic filenames and it is impossible to figure out the camera the images came from.
iWitness works well scanning all cameras. I tried the videos and those also work quite well. As I said, I have used it for 9 cameras and I could add more.
