We are installing a new bathtub and have run into a problem. Our floor is a concrete slab and the drain sits too high for our new tub. We would have to shim the tub up about 1.25 inches to get it level with the drain. Will it cause a problem to have the tub suspeneded off the floor that far? We can't change the height of the drain, right? What can I do with the huge space we will create between the floor and the tub?

If the floor is a solid pour and the raiser sticks up out of it then you're roughed in for a shower, not a bathtub. A bathtub will connect the tub drain to the raiser UNDER the pour in a 12 X 12" square tub dap-out hole that was left there by the plumber when he roughed in for a tub.
If you still wish to connect a tub the measures are to the center of the raiser, 15 1/2" off the back wall and 1 1/2" off the front plate. You will also have to break up the cement and make a tub dap-out hole to connect the drain and have the tub set level on the floor. I will not even address raising the tub, Bad idea! Good luck, Tom