I wouldn't cut them, I would just plant them and hope they toughen up. If they are the huge dahlias, you might have to stake them, but you probably have to anyways. I don't know what cutting them back would do, maybe someone else will know. But I know that my begonia that had all the eyes chewed of by a squirrel, produced more eyes afterwards, so maybe the dahlia would.

I was in an experimental mood and did sprout cuttings off a DUET dahlia tuber. (Followed the instructions from the Colorado Dahlia Society.) The sprouts snuffed it (first time so oh well) and since they were the only two sprouts from the only two eyes I figured that was it for DUET. However I kept it around and it sprouted again from the same stubs where I cut sprouts the last time. They are still pretty teeny but if my friend put it in the ground that day (as I exhorted her to do) and treats it real nice I hope maybe it will catch up.

You may cut them, it will make the next growth coming out much stronger, I do start my dahlias early March in the basement and plant them out, they fill out with the strong growth almost immediately. You just gave the rhizome a good jump start