As for ethics, as long as it doesn't violate the match rules I don't see any reason why it would be unethical. Programs can take US MDs who have already been through the match and IMG MDs in prematch positions, so it would be similar.
For practical reasons, though, it may not be desirable. These are very coveted slots that have no trouble filling in the match, and you would have to wonder why this slot was available. It may be at a program in a state of flux, on probation, or otherwise. This program may be looking for a warm body to fill a spot.
That is, unless you are a total baller. If you blew the doors off of the USMLE steps, were in the top of your med school class, and have extensive research experience, you may be able to get an offer at a good program. This is occasionally the case with IMGs. Or you may have a strong personal connection to the program (maybe one of your parents is on the staff or something).
Good luck with this.