Red oval spot on my soulder, 1" at its widest, 3/4" smallest. I've seen a dermatologist about it, and he said that it wasn't skin cancer. Opinion?

ABCD's. Remember your abcd's when thinking of melanoma. Look for moles with asymmetry boarders that are irregular color differences within the same mole diameter greater than 6mm also any new mole or old that starts to itch, bleed or ulcerate should be of concern. Another rule is the ugly duckling rule. Which refers to a mole that looks distantly different from the others on your body.
Depends. It depends on the color, the texture, the type of borders. Indeterminate skin lesions need to have a biopsy to determine exactly what they are if there is any question. Many innocent looking skin lesions can be observed on a regular interval without biopsy as long as they are not growing. Take a digital picture with a ruler next to it, and save it. Repeat every 6 months to assess its growth.
F/u with derm. Nothing can substitute clinical examination. We can not say much without examining you. From the very limited description given - it does not sound like skin cancer. My suggestion is to f/u with your dermatologist.