I have tried adding oatmeal many times. In honesty, it doesn't do much of anything for the final beer flavor or body. It mostly just mucks up the mash and makes it very difficult to run off, sometimes anyway, and depending on how much is used. I made a witbier with 50% oatmeal last year, which turned out to be a great beer when finished, but due to complications with the mash, and lack of any real benefit in the final beer, I told myself I won't be using oats never ever again. The finished beer doesn't taste oaty or have improved body or anything like that. It's just a normal witbier. I'd rather have just used wheat malt, way easier. If memory serves, the head retention wasn't even all that great, if anything, worse than anticipated. Some say this occurs due to oils in the oats, and I am leaning towards believing it.
But don't just take my word for it, or anyone else's. If you are interested in trying oats, try using a good high percentage, like 25-40% or something like that, and find out for yourself what you think.
Cheers.