Would my channeling the deep subconscious of a distant client being monitored to confirm they are in the Delta phase of sleep, show an increase in brainwave activity? If so, could that be used to help validate my subconscious channeling?

This is very much the case, and will be unmistakable. This is an experiment that can be run over and over and over again with relative ease, other than the time and cost of instrumenting people in the sleep laboratory. That this could be done in conjunction with such a facility with a simple informed consent allowing people to be tested in this fashion to check on the ability of a psychic, for example, to show up and see if there is a brainwave change. So it is simple, without any other agenda than checking the reach of consciousness and would be very straightforward by any psychology department interested in sleep studies and also the paranormal.