Hohlwein had a distinctive style, usually using the notoriously difficult (for me, anyway) watercolor medium often in flat, overlapping areas to build up images.
The quality of his work was such that his political leanings are usually ignored or downplayed by writers and critics. Critics are more likely to bring up the politics of leftist German artists such as George Grosz and John Heartfield, though seldom in a negative way. With Hohlwein, negativity would be easy to introduce, yet his work was so good that, like the case of fashion designer Coco Chanel, his views and activities are viewed with a blind eye. For example, this politically liberal artist/blogger simply enthuses about how good an artist Hohlwein was.
And what was Hohlwein's political dark side? Well, you see, he was a Nazi. A member of the party once Hitler took over Germany in 1933. Before that, he created posters in support of the Kaiser's war effort. After the Great War he did posters supporting the anti-leftist Stahlhelm (steel helmet) paramilitary organization. However, it should be noted that his political posters were "positive" in that they supported the regime without negative depictions of the regime's enemies. In other words, so far as I know, Hohlwein never created an antisemitic poster. Grosz and Heartfield, on the other hand, went to great lengths to do negative portrayals of what they despised rather than showing the presumed positive joys of a risen proletariat.
The most detailed biographical information I could find on the Web is here. And his German Wikipedia entry mentions that he was forbidden to pursue his profession until February 1946, about nine months after Germany's defeat in World War 2. So presumably the Allies noted his general support of the Hitler regime, but could find no direct connection to its negative deeds.
I begin the examples of Hohlwein's work, below, with a few of his regime-supporting works to show what they looked like. Then I include a number of the posters he made for advertisers, these being what gained him his fame.