Skeletal ones generate the PHAT in engine - usually dependent on the bones. I’m not sure IF you can actually add custom collisions to it - I really never tried it.
The main problem here is that we have no real content example to see what is what.
IF we did, I’d have probably added an exporter for it to my plugin already. Since I have never seen the kind of file they use I’m at a total loss when reading the information the docs released. (read as: I can’t even get it to work with Maya or Z brush, both of which the epic team uses as shown in various talks for the DigitalHuman stuff ).
So while it is related, particularly to what I was saying about moving away from FBX entirely - I don’t really see the plugin as being the solution to it.