Joint Deformers are OK to use if you're never going to export to a game. Most of the artists here seem to create animations for in-game use. But if you're just rendering it, then go crazy.
I have heard the advanced Skin deformations are not mirrorable, currently, although people seem to be very interested in it.
It is extremely rare for a game to support vertex morphing based on bone angle, basically because it's too little of a benefit to be worth the implementation time and the added performance cost. Games have to run in real-time, if feature X slows the framerate then it's usually dropped real quick.
support it, but our game engine isn't publicly available. In our system, you could tie specific vertex behavior to specific bone poses. In fact you probably wouldn't get a noticeable performance hit, depending on your hardware. Might be a nice demo in fact. I'm hoping to share more about the system as it matures.
Probably more real-time engines will support these things in the future, as hardware gets better.