Yes of course there are! I guess i know some of them! Here:
1) Dooglus (5000+ in my opinion
2) Stunna ( 5000+ in my opinion)
3) keepinquiet (1000+ in my opinion)
My estimation:
Dooglus: 7k+
Stunna: 20k+ he owns the biggest dice site, and over 4 billion bets, almost 4 million btc wager. 1% of the house edge, it means he at least has earned over 40k+ BTC.
Addi: 10k+ owns a casino, too
And many biggest casino owners, at least 5K+ btc.
I honestly don't know where do you guys get these figures. It is true that they own the most popular gambling sites and services but it doesn't make sense to put in there what they really hold. Intelligent guesstimate, I assume.