As far as I’m aware, today everyone makes the double dalet the same way. A minor addition was added at a later date so the back side shouldn’t look like a cross. The front side looks the same. Perhaps this change wasn’t implemented by those in Teiman who use the double dalet due to being a muslim country.
There are many major poskim, on either side and this discussion is far from new. While Rav Ulman has very broad shoulders, Rav Diblitzky, for example, who is one of the senior gedolei haposkim differs. One should follow his minhag and must consult a posek how they should be noheg if they don’t have one or if there is basis to switch.