There are no electrical code issues with what the OP proposed. The electric code and building official authority ends with the outlet.
UL, who cares, he is not selling anything.
Liability, OK, you better make it safe. He should be able to run 240V lights from this, no problem. As others have stated, the 120 loads is a bit dicy since there is no neutral.
In a 4-wire, there is neutral. He would just need to run a 4-wire "cord" instead of a regular 3-wire with the 4-wire plug. Ground would be hooked up to case, 120V loads would be hooked up to neutral, and both hots make 240V.