It is certainly acceptable to plug a device that draws 2A into a 15A receptacle.It is perfectly acceptable to plug in a device that draws less than the maximum load the breaker can handle. Look around and tell me how many devices in the room you are in draw the full 15A of the breaker on the circuit they are plugged in to. Think your cell phone charger draws 15A @ 120V? Your computer? TV? Lamp?
The key is the breaker needs to be sized to protect the wire in the circuit. The relevant parts of your statement are in bold.
As far as multiple outlets for EVSE's on a single 240V circuit, how many 15A rated outlets are on a typical 120V 15A circuit? More than one?
If you plug more devices in than the circuit will support, the breaker will trip. Try running 2 hair dryers in the same bathroom.
2 properly configured EVSE's on the same circuit will not exceed it's capacity and be no problem. Improperly configured, they will trip the breaker on a properly designed circuit.
It is not proper to install a 50A receptacle on a 60A circuit (60A breaker protected) or a 15A receptacle on a 50A circuit.
We don't have to even discuss why, just refer to the NEC.
The breaker protects the entire circuit, not just the wiring. The circuit includes the receptacle. You wire a 30A receptacle into a 50A circuit with appropriate wire for 50A and a 50A breaker and you are in violation of code. You could draw 50A through that receptacle and cause it to overheat without the breaker opening the circuit.
He can hardwire his two JuiceBox units to his 60A circuit but he can't install two (or even one) 50A receptacles to plug them in.
210.21(B)(3) Receptacle Ratings. Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B)(3), or, where rated higher than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.
The table says you can use a receptacle rated not over 15A on a 15A circuit, 15 or 20A on a 20A, 30A on a 30A, 40 or 50A on a 50A and from the above language, any circuit greater than 50A requires a receptacle >= to the circuit rating so 50A receptacles are not permitted on a 60A circuit