https://www.immigration.govt.nz/opsmanual/#66791.htm SM6.30.10 e makes me think that the kind of letter you suggest may be useful.
Other forum members have found that INZ want to know about the detailed finances underpinning the employer's company. The employer has been asked to show their business plan, etc., particularly in the state of a start-up without a long trading history to show. This is all dealt with confidentially, directly between the employer and INZ, and possibly the firm's accountant - there is no sharing of the employer's private plans and financial business with the employee. And yes, if all is found to be looking like a sound business venture, regardless of present lack of profits, people have been awarded their visas.