ethical behavior in the workplace as a whole is hard to measure and an attempt to quantify it should go through the use of combined Key Performance Indicators (KPI). However, as Ivo Carneiro de Sousa mentioned, what behavior is considered "ethical" is partly context and culture sensitive and KPIs should be selected accordingly.
It is an unfortunate fact that KPIs are underdeveloped in the assessment of ethics in the workplace and thus no consensus exists on which ones to use.
As I see it, two distinct categories of actors should be assessed separately: management and lower echelon employees.
For further insight, you can have a look at Hopkin's framework for ethical analysis which proposes guidelines as to which areas to evaluate. Empirical studies (like "Examining the link between...") also provide useful practical insight. Some more explanatory models also exist (see for instance "Ethical leadership an followers'...")
Finally, have a look at my thesis, pages 69 and forward take a stab at defining an indicator of ethical attitude (rather than behavior) for management.
You could check whether such a scale (or a related scale) is contained in my Handbook of Management Scales: https://en.wikibooks.org/wiki/Handbook_of_Management_Scales