I'll resolve the easy bit and leave the tough bone to the pros.
According to my CAA's AIP (ICAO state) it's IAS. I have the chart that shows the conventions for each of type of chart (SID, STAR, etc) but it's almost midnight and I'm too tired to scan it right now. I'll scan it in the morning and publish it here.
On the box that gives the "speed vs ROC" information it says "Calculations based on the climb gradient and IAS speed" (sic). Ground speed makes much more sense though, but maybe it's IAS since it's much more accessible at takeoff (through the ASI) and one could come across with the "correction" easily since just half a minute ago you were given wind speed and direction when you were cleared for takeoff.
G'nite all
