Is It Legal For A Supervisor To Call Employees At Home When They Have Called In Sick?

There's nothing illegal about it, but I would question the motivation behind the supervisor's actions.  You said your supervisor calls some employees, not all.  Is it possible that these employees have histories of frequently calling in sick, or have they been caught lying about it in the past?  If not, I'd say your supervisor isn't very trusting, and it could be considered harassment.

Depending on the sick call policy of the instution, there are certain employees who call out sick frequently. It is not unreasonable for a supervisor to check on an employee to see if they are feeling better to see if it is possible for them to come in at a latter time, especially if staffing is in a real crunch. For employee's who rarley call out sick, it is good policy for a supervisor to call that employee to see how they are and if they need anything. This helps promote good relations with the employee. An example would be if the employee is a diabetic and rarely calls out sick and does call out sick one day. If they dont have anyone at home with them it is a good idea to call to check to make sure that employee hasn't gone into shock or coma. You could end up saving that employee's life. This should be about careing for that particular employee not about harassment.

I think it really depends on the situation and the reasoning behind it.
But there is a very slippery road to harassment from what you have described in your question.I have seen it both ways, and must admit  that most experienced supervisors do not need to call any employee at home to figure out whether they are really sick or "sick"-they know.