Are there any safeguards in place that prevent an administrator from creating an account, using the (now known) server seed, client seed, and nonce from predicting the results and therefore reliably producing winnings over time? Sure, assuming they are an investor, they'd be stealing from themselves, if left pocket to right is stealing, but they'd truly be stealing from the other investors.
Apologies is this has been discussed before.
There are no "real" safeguards for this particular problem. The safeguard is that no one else has access to the internals of the site except the single, lone, administrator/owner/operator (and maybe amazon AWS, if they have a clue).
All bitcoin gambling sites have this same problem. All dice sites. All card game sites. All casinos. The solution is just another problem (and will reduce speed, and reduce profitability.)