In short, no.
The reason we start from a virtual reference machine with a fresh OS install onto a new, blank virtual hard disk is to keep the resulting image as free from hardware-specific customization as possible. This ensures that we can deploy that image to any make/model of target computer using a compatible Platform Pack. We don't support starting from a physical machine, or using a VM that was created using Physical-to-Virtual (P2V) conversion, because we can't guarantee the state of the deployed target machine.
For example, one could P2V a Dell OEM machine, which would have an entire set of drivers installed for that particular machine and perhaps other Dell models, as well as model- or manufacturer-specific software. Attempting to strip out these hardware-specific customizations afterward would never be as reliable as starting from a virtual environment where they never existed in the first place.
We want to ensure that only the exact device drivers from the SmartDeploy Platform Pack, which were released for the specific make/model of the target device, are used, because this will ensure that your deployments work as cleanly and as reliably as possible.