I was thinking, what if every day/hour, if the Credit Multiplier or Point Raffle, etc., doesn't have enough participants to run, the game added a random active player with the minimum amount of credits/points, for free, like a random gift.

This way, the casino games can draw more rapidly, it's a nice random gift, and perhaps reminds people that the casino games exist.

Not sure how frequently it should add someone on, perhaps hourly is a bit much, and daily is a bit slow if you need 10 people

Seems like a quick usability win to me.

Maybe every 6 - 12 hours? 

I'd go for 6 hours tbh.  Maybe the credit multiplier 6 and the point raffle the standard 12.