Can I connect a thumb drive, external hard drive, webcam etc up to a PowerLab C DFP?

This is not a recommended use case, however, the PowerLab C will act like a USB 2.0 hub, allowing any USB 2.0 compliant devices connected to a DFP to function normally on the host PC. Note that connecting other devices to the PowerLab may limit the amount of USB bandwidth available for sampling data.