Cooking Porridge in steam oven
I'm not sure what a steam oven is either, but I think I can answer: YES!

I regularly cook porridge in an unsealed/unlocked pressure cooker that has been set on a hotplate which is plugged into an appliance timer.  I put my oats and liquid into a metal canister that fits inside my pressure cooker, and I put foil on top of the canister to keep extra water from dripping into it.  The pressure cooker has a "rack" in it to keep the canister off the bottom of the pot, which keeps the porridge from burning on the bottom, no matter how high you turn up the heat.

I keep the hotplate set to just barely a boil, because I use 100% milk for my liquid and don't want it to scald.

I have the timer set to start cooking it a full 3 or 4 hours before we wake up.  I prefer to soak my grains overnight, so I set everything up the night before, and we just wake up and eat!