Trying to make a frog-like ballooning vocaliziation animation for a monster- is Blender Cloth sim the right way?

Hey @PraetorWest! Welcome to the forums!

I think from what you are describing, your best bet here is likely morph targets, which has built in support and application in the engine. Check out this documentation and non-Epic affiliated video on the subject:

I hope the above is the solution you were looking for!