Why do you think he's concerned if they "allow" it or not? The paper trail is not as obvious as you think. The insurance issues you note are not a real problem.

Why do you think he's concerned if they "allow" it or not? The paper trail is not as obvious as you think. The insurance issues you note are not a real problem. If, for example, he needed to decline health coverage at one employer he can simply say he has it through a partner. It will not be questioned. The workers comp and unemployment insurance won't matter. Multiple jobs are normal for many folks and the payroll companies and government won't care.