Rotary Burrs with End Cut, Ball burrs and Lollipop burrs all work awesome on EPS foam. I think our “flute” count is somewhere around 30 for each burr and we only use single cut burrs. Frankly, I have not found a need to deviate from a standard burr geometry, I just adjust my feeds and speeds based on the tool.
I use type XV EPS foam (3lb density) but lower densities do work, its all in your feeds and speeds. If you can get Type C bead for any density its even better.
There will be some pockets in the EPS because of how its formed but they are super easy to fill in with a variety of materials. If I can find some good images Ill upload them later to show you what you can expect