Your employer will have no access to your diagnosis. The insurance company cannot disclose any personal health information to them. All the employer knows is the amount of the premium.
The new health insurance will find out about the diagnosis if there was ever a claim filed on it- regardless of if the claim was paid. They pull records from doctors, insurance companies, pharmacies, etc. when they do the underwriting. They will know any and all diagnosis if a claim was made with it on the form.
But again- your employer has NO access to the information. It is protected by law. I need not suffer in silence while I can still moan, whimper and complain.
If this isn't what I consider soulmate crap, I don't know what is.