No matter how much will this be tested, there will be a trust issue: can you prove the gambling equipment is provably fair and will stay so?
Block hash from the major crypto currencies is lately pretty much used in draws; it could be an option for you too.

So the gambling part may need improvement on the idea/implementation part.
Then.. the investors may not care about the draw / prizes at all. They should care the projects are good, fair and will make them money sooner or later.