Not reassuring. If there's money to be made, people will try to make it. It's reasonable to assume a group of friends would take a weekend trying to collude at poker.

There are a few things you could potentially do to make it not worth their time. The first is to take money before assigning a table, and then randomly assigning the person. The second is to have the house take such a large cut that even with collusion it's not profitable.

You still have to worry about Sybil attacks. It's one thing for me and my 3 friends to play poker together and try to land at the same table. It's another for me and my 1000 bots at different IP addresses (bots who will, of course, play computationally perfect games and collude any time they are at the same table) to try and beat the odds.