Would you also refuse to pay for the healthcare of a person with a BMI of over 29? Obesity can easily cause as many health problems as smoking. And considering that roughly a third of American adults are clinically obese, it might limit your applicant pool.
For general companies, I don't think any such requirements on vaccines, smoking, weight etc. are necessary. However, I do think that in the healthcare profession, practitioners should be held to a higher standard. Not only are they in direct contact with immunocompromised people, but they should also provide an example of healthy living to the general public.