My unneutered male rabbits are fighting. Is his ear injury serious?

Ouch! Those definitely look like fighting wounds. The ear one is a little deep and could become infected. I would try to keep it clean and treat it with some triple antibiotic ointment if you can. If you see that it is not clearing up or it is getting worse, systemic drugs could be required. If you see that he is starting to scratch at the ear due to pain or bother, he is going to require an e-collar. Depending on the size of the rabbit, it may be hard to fine one that fits commercially. Fortunately, you will be able to find instruction on how to create a homemade one if the time comes. In terms of their behavior, definitely keep them separated until you get them fixed. Once that it is done, you can try to reintroduce them, but do so slowly and over at least a couple of weeks. It should be done so under close supervision as well to avoid any more bunny injuries.