What effect does a wage ratio cap have on the efficency of allocation of labour?
The effects can be quite different from a price (wage) ceiling. The baseline case where you have homogeneous, inelastically supplied labor that's free to move across different "types" of work produces no supply response in reaction to a wage ceiling, but leads to complete specialization in one type of labor or another in the case of enforced bounds on relative wages which rule out the competitive market allocation.

For companies, enforcing internal wage ceilings may be a way of trying to address problems of corporate governance - the shareholders may be trying to address a principal-agent problem by getting such a policy instituted within the company. In that case, it may well improve efficiency, but it's hard to say if there would be a significant impact on the supply of executives available for corporate management.