Same SKU but different product - Drupal Commerce
Short Answer: No, SKUs must be unique.

Longer answer:
SKU is acronym for Stock Keeping Unit. It is a specific produkt that you have have on stock, like a gray medium sized T-shirt with V-neck for men. Had it had a different size, color ... it would have been an entirely different product.

SKU's were create to be able to keep track of these different products, even if there only is a slight change. This also means that SKUs must be unique, since a SKU is the code for a specific product.

The above is general for e-commerce and originates from physical stores with stock keeping etc. Drupal Commerce conforms to these standards, and so it is impossible to create two products with the same SKU.