"different states, different rules"
Not really. CDL is federal law. The only area that the feds give the states a little say so is when the regs say.. "A State may, at its discretion, exempt individuals" But I have never found a state that does not allow exemptions where they are given the chance to exempt some.
Iowa tried to take the farmer exemption away a year or so ago. They caught so much outrage from farmers that they backed down.