Would this also count as an effective partition by Torah law for the purpose of a sukkah?

It depends whether the area between the double corner-posts is considered an entrance or a breach. If there is the form of a doorway there, then seemingly it helps for a sukkah too. In tractate Sukkah, the discussion of double corner-posts is on page 4, and there it speaks about placing the roofing on top of them, in which case there is the form of a doorway. But for a private domain on the Sabbath there is no need for roofing, and that of course does not help it count as a wall for a sukkah.

Maimonides writes as follows:
If one roofed over an alleyway that has a side-post, or over a well that has corner-post enclosures, it is a valid sukkah only for that Sabbath that falls during the festival; since this side-post and these corner-posts are considered partitions for the purpose of the Sabbath, we regard them as partitions for the purpose of sukkah as well.

It sounds from this that these partitions are not full-fledged partitions in every respect, but only partitions for the purpose of the Sabbath, and that is why they help for a sukkah only on the Sabbath. How can it be that a certain partition is considered a partition only for the Sabbath and not for other matters? Either it is a partition or it isn’t.

That is a complicated Talmudic passage in Sukkah 7a, regarding “since it serves as a wall for the Sabbath, it serves as a wall for sukkah”—see there. And in other passages as well we see that there is a difference between a Sabbath partition and a sukkah partition. For example, with partitions based on “extend upward” and “extend downward,” the medieval authorities (Rishonim) disagreed (there on page 4 and elsewhere).