I have kept pictus in most if not all of my Oscar tanks over the years. They are by far my favorite catfich to keep with O's. Make sure they have some hiding places (pictus don't like to feel vulnerable) and make sure you get pictus big enough to prevent the oscar from eating them. My experience shows that pictus will grow past the 5 inch mark in the first year, and fill out well in the second year this is big enough for all but the largest Oscars to ignore. I always buy my fish small and let them grow up together, and have never had an Oscar grow fast enough to consider the pictus as food.
Watch your pictus close for ich during quarantine, they are highly succeptable, and seeing ich on a white catfish that moves at Mach 2.0 is next to impossible.
dave