I just decided to give it a quick look using a rough system. I checked out the last 3 drafts from the last 3 worlds and counted the HS players in the top 32- there were 44, 45, and 46 respectively (each out of 96), which means a 47/53 split in HS/Coll first rounders.
I then checked the budgets, and there was a slight bias towards college scouting, which likely explains the slight lean towards college players.
Someone can do more thorough research if they like, but I would bet that the talent split is very close to, if not exactly, 50/50.