WOW! That is a very, very nice hack - very well done! Lots of work done into lots of icons, backdrops, walls, combat sets, etc....
However, I, being the anal retentive that I am, would have done a few things differently...
1. The Chinese hu-hsien and Vietnamese con-tinh look Japanese; I would have added more non-Japanese influences.
2. The monks should not be wearing karate uniforms; the sohei also had a particular look (and were armed with polearms); I think I would have done the yakuza differently, too, but....
3. As you have read from my blog already, I have problems with Oriental Adventures itself

Thus, I guess I would not be the best person to do an "as-is" OA hack for DC as I would be complaining about this and that along the way.

I.e., I don't like the Oriental dragons that much, many of the classes seem redundant to me (bushi, samurai, yakuza), etc. and everything has too much of a Japanese slant.
Still, this all makes me want to do some OA-related art

Looks like great stuff that Hans did, overall!
Also - the gargantua monster seems to look quite similar to Cthulhu - instant OA icon!

Plus, yours is more "to-scale," since DC does not have FRUA's 2 x 2 restriction...