Most of the time, I'd say yes, one to a container.
Alot depends on the size of the container as well.
I do alot of mine in a 5 gallon food grade bucket.
You can even plant
a tomato plant
in an old bale
of hay/straw too...*When I read it, they said you could put two,
one on either end of the bale*
But usually the reason you'd only put one to a container is the air circulation around the plant
Alot of times disease is caused by poor air circulation around the plant
, when it's confined
and crowded, that invites disease...