I had considered that while I was writing my Essay on the Science of Measurement Conversions as Applied to Modern Mead Making...or simply put, that post below.
I put considerable thought into it and decided that the small pellet size, if it was truly denser than water, would be enough to break surface tension. I am fairly sure that those pellets are actually more air than solid and doubt that they are actually densely packed, nuts-to-butts, yeasties. I based this on I how long I think it would take a densely packed cake of yeast to absorb sufficient water and how lumpy it would be vs how quickly the yeast actually do absorb water and create an even solution.
This being said, I reserve the right to be wrong on this and all other matters.