I have a Shohin Chinese Elm that I rescued from Home Depot last February. It is a "mass produced" tree which was almost dead and I took pity on it. I replaced the soil with a good Bonsai mix in March and have been nurturing it back to health since.
My question is about wintering. I felt that since it had such a rough time this year I would leave it outside to go dormant and get some rest. I was wondering if this is a good plan, or should I bring it in with my tropicals? Or, should I leave it out for a short time (a month or two) giving it a short period of dormancy?

The Chinese Elm can withstand winter temperatures like no other; also in the circumstances you described I would leave the tree outside.
Perhaps it would be wise though to protect the tree a little bit better than you would normally do, since it has been repotted early.

Hope this helps!