offset soundhole bracing pattern

if you were to do a offset soundhole, could you just use a traditional fan bracing or must be kasha style?

The only 'must' I can think off in regard to bracing patterns is that:
1- The soundhole has adequate strength around to it not cave in and,
2- The top has enough bracing strength to not distort beyond what is acceptable.

So no, it need not be kasha, or any other, bracing pattern.

Just like Beau said.

You need to think of the forces that are acting on the top and brace in a manner that will control them sufficiently to withstand them, without being over braced. The rest is where the fun and magic comes in.

If you google "offset soundhole guitar bracing" and go to "images" you will see a lot of different bracing patterns (guitar will give a lot more hits than uke). If you are thinking of putting the soundhole in the upper bout, like many do, then it is under far less stress than in the center, and does not require the heavier transverse braces, either at the soundhole, or at all. Most of the force was from the string tension and the fingerboard trying to push the top in. A center hole is a major weak point that required more structure. The lesser tension of Uke strings allows for less bracing. So, the fans can be extended past where the soundhole would be.

There is no one way to do this. You just want to support the top, and transmit the vibrations.