I've searched the rules forum for information about exactly how the combined units are supposed to work and it seems that previous topics left the issue clear as mud. So:

When you purchase a solo Commissar for an SSU army do you either:

1. At list creation time buy two identical squads and attach a commissar to them to form one large 11 man unit. This unit counts as a suport unit and so fills one of the platoons 1-per-2 sections support slots.

2. At list creation time buy two identical squads and attach a commissar to them to form one large 11 man unit. This unit counts as one of the platoon's sections, but is treated as a support unit for scenario purposes (literal reading of the Commissar rule from DW:CZ pg 18)

3. At list creation time buy two identical squads and put them in as sections in the platoon. Also purchase a solo Commissar. At deployment time decide to attach these two squads together with the Commissar, forming one large section and incidentally reducing the number of squads you have by 2 for initiative purposes.

Has a difinitive answer been reached that I missed. I don't see anyting in the errata that clears it up.

a single squad that is treated as a Support section (for the purposes of some deployments). The squads you combine do not need to be from the same platoon, but must have the same upgrades.