Are you asking a vector program to animate, efectivly supply, the "blue screen" back ground animation for
the animated image supllied by bryce...?

if it is even possible  to pull each frame of the bryce animation  as it's own file.
yes you could record an action that uses the alpha channel as a MASK to eliminate unwanted image area  and save that frame as a png file.. save the fram and start procesing the  next one...

From what i know of dreamweaver each transparent image .png would have to be imported as a seperate entity.

i would think many frames of image would take up alot more memory in flash,

Are you taking this to web? HOw many frames  can you get away with? will  the frames take an immence amount of "loading..." time due to the file sizes ( in  dimentions and memory) of the "bryce/photoshop" frames