Well, you may be in luck. It looks like there are a change in value for oats, which has happened with some foods because of additional research/testing. The link will take you to the most up-to-date information:
So, if you are an O secretor (80 percent are, and the general instruction is to follow the secretor plan until you get tested and find out for sure), go right ahead and enjoy your oatmeal!
As you will see, though, it doesn't give a reason why oats are avoids for type O non-secretors (not that the 'reasons' always make a lot of sense even when they are given!).