When Superman Hulked up (Big muscles and all) on Kryptonite X and tried using Parasite to get rid of the excess energy, he accidentally killed him with his heat vision, intending to only use a little bit and not being able to control himself. At normal levels, his heat vision is hotter than the sun, and this clearly wasn't just a normal HV burst...
So it flash killed Parasite. But, he immediately reformed his body while sucking Supes dry.
Since Hulk's usually radiating Gamma energy all over the place now, Parasite could just suck it out of him without even touching him, likely.
Some of these fans haven't heard of Half-Life, who had powers that functioned in similar fashion to Parasite except he exclusively absorbed gamma radiation. He gave the Hulk a good scare in their encounters, and even was on the verge of winning once.
http://en.wikipedia.org/wiki/Halflife_%28comics%29
If Parasite can subdue Superman, Hulk would be a similar challenge. 50/50 draw.