Is it ethical to put a surveillance camera inside a lab
This largely depends on disclosure --- in cases where you record employees at work there are ethical and legal obligations relating to notification and disclosure.  The legal rules depend on your jurisdiction, but in most jurisdictions this situation is regulated by some kind of legislation on surveillance.  (E.g., in NSW in Australia this would be regulated by the Workplace Surveillance Act 2005.)  To check on the legality of this practice you should consult relevant surveillance legislation in your jurisdiction.  Regardless, your lab leader should certainly contact the university legal counsel before installing a surveillance camera.

As to the broader ethical question of surveillance (as opposed to its legality), there is a reasonable literature on this question in the business ethics journals (see e.g., Ottensmeyer and Heroux 1991, Fairweather 1999, Halpern, Reville and Grunewald 2008, and Hadjimatheou 2014).  I will not attempt to paraphrase this issue here since it is a large issue which is best understood by reference to the literature.