I used my rice cooker for oats...twice. Both times it was a huge disaster! It was really really gross, gummy and slimy. It made a mess of the cooker and the resulting oats were not edible (unless I was willing to scrape them off the counter top!). And I do have a 'porridge' setting!

I have had the best luck with either stovetop or in the slow cooker in a steam bath (the oats sit in a bowl inside the cooker in a couple of inches of water). The best part about this method was that they cooked overnight and I had hot oats when I woke up with no work (and easy clean up).