If you think it helps you, do it. As a startup founder, you should have enough critical thinking ability and confidence in yourself to know what works for you and what does not. However, I see no reason to be open about it, especially to investors. No investor is going to say "he smokes weed, therefore his company has a higher chance of being successful."

So smoke if you want to, but keep your mouth shut when talking to people with money.

This is a pretty good life rule.