Nope - they don't... I thought maybe they did and I'd just been too busy getting killed to notice
BUT you can reproduce the situation in the editor.
1. Create an infantry squad with you as the leader.
2. in Preview - order "Form Line"[8,7], order "Fall Back Into Formation"[1,1], order "Halt"[1,6].
3. now move out in front of the squad, turn around and check their spacing, even # soldiers will be on your left, odd # on your right.
4. Abort back to editor
5. counting from left to right, edit soldiers #2, #4, #5, #7 and set their Health/Armor to zero.
6. in Preview - repeat step 2 and you will see the gaps. Even if you continue to move and order [1,1] they will hold their original formation spacings. No gaps closed.