Could answer a few questions for me so that I can better help you?
Is he scratching at the area with his back feet?
Is he eating and drinking normally?
Does he have any other health problems?
Thanks for answering my questions.
Good to hear that he is eating and drinking normally. You did not mention what it was that you are using to treat the ear mites, but know that most of the over-the-counter remedies for this are not effective, so if you have not done so already, get something from your vet rather than using these products.
It is most important that these sores on his neck be kept clean and prevent further injury to them from scratching. I would recommend cleaning them wiht just water twice daily. Don't use hydrogen peroxide as this is too harsh and will actually delay healing. If he is scratching at the area a lot, we need to do something to help prevent this. He may also be scratching at his ears because of the ear mites. This is a difficult area of the body to prevent scratching at - I would try maybe putting a kerchief around his neck to try to protect him from getting to the sores with his back feet. Not all cats will tolerate this, but it is worth a try. It needs to be tied tight enough so that they won't be able to catch it on anything as that could be dangerous.
It is okay to use Neopsorin on the sores. I do not use a lot of topical ointments in animals because that tends to make them want to lick it off, but if the sores are around the neck, he probably cannot reach them. It is more important that they be kept clean though, so even if you decide to use the Neosporin, be sure to still clean them twice daily.
If there is any question about whether the area looks infected, you should have him checked by your vet so that he can be started on antibiotics.
I hope this answers your question. If so, please click Accept. If not or if you need additional information, please let me know.