You can use which ever one you like for reheating. I find the oven to be fine for most items, but at times, the "O" is busy with other items, so off to the smoker we go. Also, the smoker may be a larger capacity and handles it without crowding things so much. The only thing you may want to do is rotate the smoker grates for multiple items, as food and pans on lower grates can catch a lot more of the heat and baffle the grates directly above it. The larger the item, the more of a baffling effect it has. Always double-check you internal temps when reheating to be sure you're getting them heated evenly...once or twice during the reheat is sufficient, then one last check at the end just to be sure.
You had a nice smoke going there today...happiness is a full smoker!!! LOL!!! Ah, pepper stout beef...read about that a while back...still haven't tried it yet...one day, soon, I hope. Let us know how everything goes. Any other questions, give a shout.
Eric