Yes, I understand it is okay, because it cools quickly and the beer has plenty of yeast. However, I always let it cool first, so I do not have first hand experience.
I usually just boil my priming sugar. I let it cool for a few minutes but definitely not cool,it way down. Dump it in and rack on top of it. As you start adding beer it cools it down. Do not worry ther is still plenty of yeast to carb the beer up. 400+ cases and no issues.
Mine cools for half an hour or so, but is definitely still warm when I rack the beer onto it. You're talking about 2 cups of warm priming solution vs 5 gallons of beer, so it's not going to have a huge effect temperature wise.
I boil mine and then add it to the bottling bucket when I've racked about 1/4 of the brew in. That way I can say, "No yeasties were harmed in the racking of this beer."