Here's a clip from Sedlar's film which shows first issue of the magazine titled "Ustaša" which Pavelić began publishing in the spring of 1930 (skip to 3:13). Although stylized, the header clearly shows an asymmetrical "U" with a bomb in it (symbolizing revolutionary struggle).
At 3:37 in the same clip a magazine cut out showing the UHRO organization logo is shown as printed by them - an asymmetrical "U", a flaming bomb inside it and a chequoy on the bomb. It looks just like the one Nanin7 had made and DIREKTOR removed (bar the dark-blue color which Nanin7 used to fill in the letter U). The original is black-and-white but the letter itself clearly wasn't meant to be black.
At 5:03 in the same clip the front page of the organization's statute is shown, again, with the same logo as described above, dated 1932.
At 5:22 the narrator talks about the organization logo directly and says that "The "Ustaša" was defined as a revolutionary fighter, also indicated by their logo, which first appeared in the masthead of the magazine "Ustaša" in 1930. Inside a blue letter "U" a silver hand grenade is depicted, with red flames coming out of it. In the centre of the bomb a small Croatian coat of arms is shown, with the top left field in silver." As he is saying that yet another picture of the logo is being shown (this one seems to be an enamel badge). The text btw was written by one Mario Jareb, a historian who wrote several books on the history of the Ustaše as well as one on the history of Croatian national symbols.
At 5:55 in the same clip front page of yet another party newspaper titled "Nezavisna država Hrvatska" (published in New York, Chicago, Pittsburgh and San Francisco), with the same logo shown, this time in the form of an initial in the main headline, dated 1 May 1934. 
So I don't know how much more official can it get. As for the "several variant" thing - I can only assume they dropped the bomb once NDH was established (since per their logic, the revolutionary struggle has achieved its goal) and replaced it with just a chequoy which was then used as a state symbol later on. I've never seen a cross in combination in contemporary use, only in modern far-right graffiti, but I may be wrong. Either way, this article is about the Ustaše party/movement and this version is the closest we will ever come to what was their official symbol. Only the shade of the color blue can be considered debatable (I tend to think it was probably lighter blue than what Nanin7 used).  (''talk)