I am installing a Broan Allure I range hood but the house electrical is on the left side of the duct work and not long enough to reach the knockout for the wires which is on the right side of the appliance. What can be done in order to make this work? Is splicing the wires an option?

Yes, but not behind the hood.

One solution will be to get the cable up into the upper cabinet above the hood, assuming there is one, and install a junction box inside the upper cabinet.