For a whole paper on the subject:
The Value of Oats in the Nutrition of Swine
by HE Woodman R E Evans & A W Menzies-kitchin
The Institute for the Study of Animal Nutrition, University of Cambridge - 2009
That link might not work outside of the Cambridge domain, so their conclusions were:
a) oats aren't as good as maize or barley, but quite usable
b) you're OK feeding oats & hay with nothing else.
c) whole or coarse ground oats aren't digested very well (Mac's point I think, from the other end so to speak) but they should get around 90% of the energy even with whole oats.