No, you are not. Employees do not have an obligation to act purely based on morals without considering the balance of potentially very one-sided legal and financial risks to themselves.
These are professional investors with the means and the obligation to do their own due diligence. They don't need individuals making potentially life changing sacrifices in order to save them some money.
Fraud is only fraud if a judge says so. Until then, it's an accusation. The accused will defend themselves and potentially hit back at the accuser.
I would take legal advice, both on whether I have a legal obligation to report what I have seen and on how/if it can be done without taking on outsize risk myself.
Edit: Consider the moral situation from the other end for a moment. I'm a small investor myself, far too small to even be allowed to invest in venture capital funds.
Would I want some employee somewhere to take potentially life changing risks in order to protect me from losing a percentage or two of my money? Certainly not. How could I expect anyone to take on far more risk than I'm taking myself?
What I would say to the employee is, stop contributing to the deception! If there's anything more you can do safely, I would be grateful.