Ground effect in this case would be virtually non-existent because of the extremely small disk loading in the case of those miniature jet engines. The ratio of the jet diameter to each jet's height off the ground shows that the ground effect is pretty small in this case. Probably less than 1 percent thrust increase in the case where the jets are attached to his arms and back according to this graph: http://www.copters.com/aero/pictures/Fig_2-39.gif (This graph proves that he's getting essentially zero ground effect.)

The actual exhaust velocity of those jets is extremely high, and for a lot of the video he is holding the jets at a significant angle with respect to vertical, giving cosine losses. With a thrust to weight ratio of over 1, I have no doubt he could achieve extremely high speeds (yeah, 200mph or over) given even a slight amount of lift from his body in horizontal(ish) flight.

To get ground effect with something like that you would have to interrupt any recirculation (see helicopter ground effect). Just looking at the dimensions of everything you would think that the possible ground effect (recirculation) zone would be less than half a metre and the engines are higher off the ground than than that.

Does ground effect apply, when your lift is from a narrow jet rather than a wing? I believe ground proximity presents a problem for VTOL jets, at least in part due to recirculation.