In the early days of the Hayes code, were there filmmakers that actively resisted it? What were some loopholes and work arounds for those insistent on making the film they wanted?

Many of the guys testing the early limits of the Hays code were intent on making money. The films they wanted to make would show as much skin as possible, but would still be allowed in theaters. Nudity was forbidden, but there was this:

"VI - Costume ... 2. Undressing scenes should be avoided, and never used save where essential to the plot."

So the wizards of Hollywood came up with... Jungle Movies. For example, it was essential to the 'plot' of "Tarzan and His Mate" (1934) that Maureen O'Sullivan and Johnny Weissmuller wear skimpy outfits. They were in a hot tropical forest! Many, many other jungle films drove through this loophole in the 1930s.

(This kind of thinking was revived briefly in the early to mid 1960s with 'beach movies', like ones with Annette Funicello. But the Code was on its last legs by then anyway.)

As far as an artist wanting to express a vision in conflict with the Code (as opposed to just selling sex), a good example is Bill Wilder and "Double Indemnity" (1944). Double Indemnity was one of the first 'film noir'; it had murder, adultery, crime, suicide... all potential problem areas for the Code. This was mostly addressed by strongly suggesting things with dialogue and with inferences. You don't get to see the murder, but there was no doubt it occurred in the room. It was still a very controversial movie, but it made lots of money so the studio was happy.

Source: https://muse.jhu.edu/article/395849/pdf