Are there studies that empirically validate results in contract theory?
An excellent (if slightly old) survey on the empirics of contracts can be found in


  Pierre-André Chiappori and Bernard Salanie (2003) "Testing Contract Theory: A Survey of Some Recent Work", in Advances in Economics and Econometrics, vol 1, M. Dewatripont, L. Hansen and S. Turnovsky eds, Cambridge University Press.


It is mostly non-technical. Bernard Salanie (literally) wrote the book on contract theory. An ungated pdf of the chapter is available here.