I put in a bug log a while back reporting that UGS was improperly rendering rotary gcode.  Well they really came through and put in a fix a few weeks ago, and you can now download the fix from the nightly build.

Here it is rendering my bat project, you can see it is doing a lot better than previously.

It is much better, but it is still not perfect.  Here I'm trying to make a 80 degree spiral but instead the x and a axis are moving one after the other.

And here I have sub divided the spiral into smaller segments.  You can see the intended shape better, but it is still just stair stepping rather than spiraling.

You can download the above example code here.