Is it safe to eat raw, soaked grains and seeds such as buckwheat? I was wondering about the safety of frequently eating grains or seeds that have been soaked overnight, but not cooked. I'm thinking about buckwheat, barley, spelt, rye... 

Soaking in water with a bit of vitamin c or apple cider vinegar should reduce the phytic acid content enough. Is there anything else that would be of concern ?
It's not uncommon and quite safe, but then the ones I have soaked (and sprouted) are not the ones you have listed. I have sprouted black sesame, fenugreek and some lentils. I use a lot of information from sproutpeople. You could try them.