What kelly are investors exposed to when they receive 0.75% of the house edge but a single player constantly bets to win 1.5% of the bankroll?
Without knowing the house edge in this scenario, it's not possible to compute.
If you are referring to bustabit, I believe it launched such that the worst case for investors (assuming multiple account aiming for max-profit) was a ~2x kelly. After the update, it was changed such that the worst case would be ~1.5x kelly. All of these risks were clearly documented
When you minus the dilution fees from the original investment, what does the kelly become greater than?
That doesn't impact the kelly at all, as the site is risking based on your post-dilution fee bankroll.