I've done a steamed sponge in a dutch oven.
I put the mix into a bowl and poured water around it, then put it into the coals.
As long as it doesn't go dry you should be fine.
If you could support the pudding basin off the bottom of the DO, on a trivet or some such, it would probably be ok even if it did boil dry - the DO could cope with the heat and the pudding would bake.