If I do a single slash score to try to get an ear on a boule, much like the one done for batards, will the boule maintain its round shape?
If you bake on an open surface, then ... it is likely to not maintain a round shape.
which talks about symmetrical scoring.
However, even for a non-symmetrical score....If you bake in a dutch oven ... and ...the pre-baked dough is sized to fit up against the side of the dutch oven, then ...the side of the dutch oven will keep the circumference in a round shape.
…with a single slash, like scoring a baguette, will yield a loaf that is elongated, similar to a batard but not so extended.