A: If by wage earner you mean non-exempt, normally it is only non-exempt employees who are required to clock in and out. But there is no law prohibiting an employer from making exempt salaried employees clock in and out.
A: If the employer is counting the snow days against your FMLA leave, you cannot be required to make it up. But the employer should not count the snow days against your FMLA leave, in which case you could be required to make it up.
A: The answer depends on whether your employer has informed you, in writing or otherwise, that you are not entitled to come back on the property and your paycheck has been mailed to you. A finding of trespass turns in most states on whether you have been notified not to come onto the property and whether you have a legitimate basis to come on to the property. Normally, coming to pick up a paycheck would be a legitimate basis to come onto the property unless you have already been told that it will be mailed to you and that you should not return. If that is the case, the safer course is to wait for it to be mailed. If you do not receive it, report it to the Dept of Labor as nonpayment of wages. It is best to avoid physical confrontation.