No, the type of braking system has absolutely no bearing whatsoever whether a vehicle requires a CDL or not.
Yes, in Michigan, you are required to have an air brake endorsement to drive a commercial vehicle with air brakes. This endorsement is obtained by passing a written knowledge test specifically for air brake systems.
Air brakes are entirely irrelevant as far as whether or not that vehicle needs a CDL is concerned. The only time you need a CDL to drive an RV is when you're operating it on a for-hire basis, either as a driver for hire or as a transporter.
If it's a job which requires a CDL, then you cannot have the "no air brake" restriction. There is no such thing as an "air brake license" in the US.
Only if it's a vehicle equipped with air brakes.
Air brakes have absolutely NO effect on whether a vehicle requires a CDL or not.
If it's not a type of vehicle which is exempted from CDL requirements under the FMCSR (farm vehicles, recreational vehicles, military vehicles, and emergency vehicles), then yes, it requires a CDL. It's not the air brakes which make it require a CDL - it's the weight rating.
There is no air brake endorsement - if a CDL driver does not complete the air brakes portion of the written test, and test in a vehicle equipped with air brakes, then they get an "L" restriction on their CDL, prohibiting them from driving commercial vehicles with air brakes. For some bizarre reason, this only applies to CDL drivers - an F750 equipped with air brakes and grossing at 26,000 lbs or less does not require a CDL or air brake permissions. If it's loaded to the point where it weights 26,0001 lbs or more, now it requires a CDL without an air brake restriction. If it weighs under 26,000 lbs. but is designed to transport more than 15 persons (including the driver) or is transporting hazardous materials, then again, it'll require a CDL with the appropriate endorsements and no air brake restriction. But Joe Average can drive around in a U-Haul or RV weighing significantly more than anything they've ever driven in their entire life, and equipped with air brakes, and it requires not one additional bit of licencing or training for them to be able to do this.
Yes
If it's a registered farm vehicle, then typically, no, although the licence requirements for vehicles exempt from CDL regulations vary between states - some states may require an upgraded non-CDL licence, and may require the air brakes test to be taken. If it's a commercial use vehicle, and not registered as a farm vehicle, then they would need a Class A CDL without an air brake restriction (there is no actual air brake endorsement).
Air brakes have absolutely ZERO determination in whether or not a vehicle requires a CDL.
When you got your CDL did you take the road test in a air brake equipped vehicle? If you did not then you have to retest to add air brakes. Not the whole test just the air brake portion both written and pre-trip portion of road test.
The braking system doesn't determine whether or not a vehicle requires a CDL.