Most auditors are discouraged from investing in stocks and funds where they are privy to informaton on the inner workings. This borders on insider trading.
A Big-3 audit firm for example, has relationships with 20 AMCs in the US and provides advisory to another dozen or so. One of their senior employees (and his son) had to face charges of insider trading and SEC settled charges against them in the US.
Even in India when i speak to some such firms the request from them is to ensure that their employees are kept away from specific funds and stocks that they have a relationship with them.
Now for an individual auditor, the above ought to apply though implementation of the checks may not be easy. It would be prudent to make adequate disclosures and stay away from any conflict-of-interest* positions.
* ps: Most ‘advisors’ in India who sell commission heavy products are prone to conflicts of interest. As an investor you are better off engaging a SEBI registered investment advisor who is required by law to avoid such conflicts of interest.