Microstrip,
As long as the chassis is earthed I can`t see the problem with safety;just think lots of cheap consumer grade electronics in plastic cases don`t have a earth connection,are they unsafe?
No, they have double insulated transformers of low power and are classed accordingly. Also there is no shock hazard in a plastic box.
The critical aspects are the reliability and resistance of the connection to earth - I am sure that electrical codes and regulations specify it clearly.