You need to check with the warranty and the manufacturers instructions of the brand and type of blown in insulation you are going to use or check with the blower/contractor for installation and warranty if you aren't doing it yourself.
Steve was going to check with the manufacturer of the brand he uses but hasn't reported back on it yet.
I'm personally not aware of any problem blowing a non-flammable insulation on top of junction boxes over the porcelain pull chain type ceiling lights (the heat from the light is concentrated and dispelled in the room and not in a recessed can inside the attic) but then I wasn't aware of the 18" rule for the product Steve was using and he hasn't really said what brand and the exact type it was.
I know it isn't a problem with fiberglass batt type insulation over junction boxes. Fiberglass can be against and cover IC rated recessed light cans but can only be placed up to 3" of and not cover non-IC rated recessed light cans.
In regards to a blown in insulation manufacturer's warranty and instructions with the 18" distance from lights, it sounds like a way to avoid paying for fire claims. But if they don't trust their insulation within 18" of lights and they probably have the research and claims data to support it, then I wouldn't use such inferior quality and fire hazardous insulation like that. The stuff may not be as fire resistant or non-flammable as they may otherwise claim.