Sorry, I can't help you with EEG. In MEG, one can use this band, too, I presume, albeit we did use the "classical" bands (8-12 Hz, 14-30 Hz), back in the 90s. I admit we never did organise the data so it remained unpublished. As for EEG, it should work, tools the frequency of spikes is closer to this band. When you look at ECoG, than the frequencies may be even higher. The hippocampal theta in animals may well be an alpha in healthy human, but there should be higher frequencies detectable in humans, too. It may be that the higher frequencies are prone to other conductivity-linked artefacts as lower frequencies, and that they more dampened by the tissue between brain and electrode.