Mash em if you got em! Steeping is better than nothing, treat them like any other specialty grain if your doing extract. If you will be doing a partial or full mash, beware it can get gummy.
You'll get very little out of them just by steeping. Greater than zero, but I'd argue so little it's hardly worth bothering with. They really need a mash.
Not sure you would get much conversion just steeping him either...
On topic:
I did Deathbrewers Easy Partial Mash with one large pot and one tiny pot (normally for boiling pasta)... Basically, steeping and partial mashing aren't that far off... just kinda like steeping more grain.
Again, take my advice with a grain of salt as I am a certifiable noob.
Steeped oats will not contribute to the fermentables. You will get much of the mouthfeel and body from just steeping, but you will also have some starch. Not a problem in stouts & such.
Mini-mashs are extremely simple and will convert the starches.