Can I glue a sleeve over a cracked dishwasher inlet line on my brand new garbage disposal unit?
With your inlet line cracked it might be possible to repair depending on how much of that inlet line exists.

as an FYI fro a better route: If you purchased that thing via HD or Lo - take it back for an exchange - they generally will do it. even if you are outside of 30 days. Damaged in shipping file a damage claim with the carrier.

Now on to the answer if the better route is not possible for you.

Repairing ABS plastic is not the easiest and I do not know if ABS is weldable like PVC pipe is. 

What I would do is insert a small piece of Thin Wall copper pipe on the inside of the inlet for support and on the outer side maybe fit PVC or a tight fit Rubber Hose over the outer side with and connect my dishwasher outlet into it. You can use a high temp gasket sealant with this setup as well but don't use too much. Make sure you provide some strain/stress relief on the pipe as well.

See below for an example.