I am not so certain that you will find an argument in favor of honesty in numbers. Logically, though, it must be preferable to deceit.
This is all very clever--the machinery, and allowing us to experience the dome while keeping us confined--but what is your motivation? [Not that he expects an answer. It's worth asking?] It would almost be simpler, I think, to create an actual dome and put us there than it would be to sustain our bodies and project our minds into a shared environment, unless you have a reason to want us comatose.