Let's ask it another way, would it be unethical for a company to hire you, promise you that they'll pay for your tuition, give the leadership team hefty bonuses during a period of declining growth and profits, and then lay you off 6 months into your contract? Yup.
Do companies do it all the time? Yup.
You're the CEO of your own career. Do what you need to do to maximize your earnings and growth. But, also, don't burn bridges when you move on.