Yes I do a grain steep. I have used Oatmeal in my stouts but it was the type of oatmeal that did not need to be mashed. Do you ever use brown sugar, molasses or maple sugars in your stouts? I have used Golden Naked Oats, Rolled Oats along with Special B (Castle) as steeping grains in past Stouts.
You can use maple syrup, brown sugar, etc...in any brew...but if you want those things to add flavor...well...
If you put any of those into a fermenting bucket they will not add flavor. They will only add ABV. They are all 100% fermentable. u want those flavors u either have to kill the yeast with perservatives or use an extract. Otherwise you will just increase the alcohol content.