Assuming the hoverfans could produce sufficient lift (as in thrust), yes a loop is possible. For the most part, the fans would only produce sufficient lift to provide the air cushion.

But again, assuming sufficient lift...terrain wouldn't be as much of an obstacle either. In other words, the thrust would be adjusted for more "lift" meaning more ground clearance.

In my SF universe, hoverfans are variable thrust devices that are used for both the air cushion as well as maneuvering and braking, meaning fans on one side would emit more thrust to pitch the vehicle into a lean for a turn, or the fans in front would spit out more thrust forward for braking. In other words, the hoverfans don't just lift the vehicle off the ground, they also serve to maneuver it (as opposed to stationary hoverfans along with aft fans for thrust and directional vanes for maneuvers and air brakes to slow it down). So a stunt driver would be able to perform a small "loop" on that premise, but it would be something performed starting at a standstill --- as in "maximum braking at a stop" to pitch the front up, followed by a "burst of forward acceleration" to execute the loop. I just wouldn't permit the loop while in motion as my fans don't work that way.

OTOH I also have "additional thrust" fans for offroad use, meaning a higher air cushion for the nastier terrain. But again, that only puts the hovercraft in a higher position for such use, not so much as to provide more thrust for the loop maneuver. "Street" hvoercraft sit at a 30cm height as suggested in the rules, the offroaders simply sit at 60cm instead and have better modifiers for the terrain (which actually still suck for rough terrain compared to say...an explorer, just not as much as the modifier for a standard hovercraft).

I'm not overly fond of Zeb's Guide...nor do I have any qualms stating why. 

My SF website