I tried powdering them in a coffee grinder a few times. It works but there are few disadvantages.
One is after you've ground tem up..they take up way more volume as the powder is extremely fluffy.
The other is when you add the powder to shakes in any decent amount, it makes the shake really gloppy. It's way easier to drink down the whole oats IMO.
Some companies are adding powdered oats to thier formulas..but of course they charge for it so why bother.