Depends on your priorities, I guess.
Yes, the tire monkeys will not be happy. The Hoosiers run quite wide for their listed size, and fitting them on 5.5s will be a challenge.
On wider wheels, the sidewalls will not bulge out as far. This gives you more predictable response from the tire, and usually less deformation. It also widens the contact patch, which tends to give you more lateral grip.
I forget, are your fenders modified to fit wide rubber? If not, you may not be able to run the Hoosiers on properly-wide rims.
The tires will very definitely work better on wider wheels than the 5.5s. Running them on wide heavy steel rims sounds to be a win over narrow but lighter wheels (especially because you've got some torque to push the weight around). If you really want to go for maximum performance, find some 7s or 8s that are nice and light and use them. Not cheap, though.
Or you could just run them. Says the guy who drives to the autoX on hard-compound street tires (in a sticky-tire class), doesn't even check the pressures, and just runs them.
--DD