Is there any proper way to address rude behavior?

[Revelty]

My husband has been mentoring one of his employees for over three years. My husband wrote a 2 page letter of recommendation for his employee who was applying to business school, helped edit his business school application essays, let him work flexible part-time hours while continuing to give him full pay and encouraged him in every way possible, including letting the employee use company resources for business school projects and offering a promotion upon completion of his degree. The employee has never even once thanked my husband. The employee graduates this month with his MBA, and an opportunity for promotion in my husband's company. My husband has privately told me it really bothers him that his employee has never said anything by way of thanks, but thinks it's rude to mention it. Now it so happens, the employee's best friend is also an acquaintance of mine. Would it be rude to ask my acquaintance (who works with the employee) to drop a hint that the employee should thank my husband? I feel like there must be some way to let the employee know so that my husband will get the thanks he deserves and will also think that the employee thought to thank him without finding out I was behind it. I don't think I should tell my husband's employee myself because I don't personally know him that well, but there must be something I can do to make my husband feel better?