The other answers are missing the main point, which is the "ethically" bit. Without that, it is a tautology. Of course good ideas from one domain can always be applied in another if they are applicable.

The ethics part is about the inherent destructiveness of war.

And yes, business has a destructive side. When you win, another business likely lost. When you laugh all the way to the bank, somebody else possibly cried all the way to bankruptcy.

Is it ethical?

It is if you believe in creative destruction and a variety of social darwinism. If not... well, there aren't many choices for you, since communism didn't work out. So far, the brutal game is the only game in town.

Most laws governing corporations are designed to address a lot of the cruelty that would happen if pure business-is-war thinking were allowed. These include unemployment benefit laws, patent laws, limited liability, the ability to declare bankruptcy, preventing businesses from using violence, contract law and courts and most importantly, antitrust (which would be like saying, in war, that no one side is allowed to win outright)...

But even with all those protections, there is a lot of room for legitimized brutality in business. A big company may legitimately be able to put a small one out of business by undercutting it and sustaining losses for longer than the small business can, despite selling a crappier product that hurts the consumer, and then raising prices after the competition has been destroyed. Should it? The corresponding military strategy is attrition.