Decades ago, such a situation would surely be called extremly unethical and the business environment would have condemned it. Nowadays, however, such situations happen often and no one is surprised. The "business is business" approach is popular, and the boundaries of decency are often blurred.
In order to stay on the market and be better than the competition, you have to constantly look for new solutions. One company optimizes its processes, another develops its existing solutions, and yet another tries to offer an employee of another company better conditions and wage in exchange for changing the employer. Such situations are so popular that it is difficult to talk about a lack of ethics here. There are much more controversial practices.
