The TPA theme is less-encountered in Hawaii. In California, there's a mix; but it still is predominantly Hawaiian. The East Coast seems to lean more towards TPA.The impression you have is pretty much the impression I have with some exceptions.
Are there similar theme associations in Japan? The impression that I get is that it is predominantly Hawaiian, with an infusion of Modern Jazz and Pop.
As an instrument, it is not taken so seriously. In a group of people recently, one person introduced his friend as being able to play the ukulele really well. Most listening laughed. I remained cowardly silent.
Hawaiian is very much in the forefront of many--that and Takagi Boo, whom I wrote about 22 June last year.
Ironically, Jake Shimabukuro is one player that seems to be diversifying that image. Tsuji Ayano is well-known here more as a pop musician than as an ukulele-player.
Ohashi Hidehiko has put collections of music such as bossa nova for ukulele. There are gobs of books available for pop songs, some jazz, bundles of Hawaiian, and even some classical music. But, as for TPA, it is a bit sparse, with perhaps the exception of Janet Klein fans here and an Osaka-based group. (Their name escapes me right now, but I think I have made reference to them somewhere.)
I guess that in some ways that is not too surprising. During the time TPA was big in the US, Japan and the US were not in the best of terms and it wasn't a particularly happy time for Japan in general.
Personally, I would love to get my hands on some Fats Waller for the uke.
One of the exceptions I hinted at above was enka (Japanese country??). Some of the people who started playing ukulele during its first boom here are getting older and settling back into some more familiar music. I know several of these that play enka on the ukulele. To me that would be like playing blues on the bagpipes, but to each his own.
PS Sorry to take so long in getting back to you!