No it is not. Melenaoma is skin cancer so therefore it would more than likely be the skin under the toenail that is cancerous. If the cancer was in the toenail that would be bone cancer since nail is bone. If it is something that is scarring you you should consult a physician.
A toenail cannot, itself, have a melanoma. Melanoma is a skin condition, and toenails are made of a different material. It is possible, however, for the flesh underneath or around the toenail to have it. Thus, it might look like the toenail has a melanoma, but the actual condition is underneath or right next to it.