Could I drill with an endmill?

It would not make sense to drill a hole with an endmill, although end mills can be used for creating circular pockets of specific sizes. For pure drilling of “standard” sizes, you would be better off using a drill bit, which is specifically designed for drilling. Since the cutting lips at the end of an end mill are angled up as they approach the center of the tool, the cutting forces travel outward, causing the end mill to wobble. The forces on a drill travel through the center of the tool, so they balance out. End mills are better at handling lateral loads, whereas drill bits are designed to plunge straight through material.