If any information which is not disclosed to the client in fear of invoking a moral hazard, will it be against the utmost good faith or not?

The utmost good faith depend solely on the insurer and insured ethics. So, if the information not being disclosed affect the decision of coverage to a point where denying coverage might be an option, yes it is against it. 

Some information might be considered common knowledge and the insurer is not obligated to explain it nor mention it. but again, if the insured ask about it, the insurer needs to explain it in depth.