for casino, you also can invest in Bitdice.com too, they are accept btc too as investment.
Poloniex and Bitfinex are Exchange Sites, and while the BitDice.com is a unpopular gambling casino website. and think they have the new website " Stage.BitDice.com "
There are too many gambling website that offers invest like cryto-games.net 777coin.com Bitvest.com Rollin.io and many more.
its true that poloniex and bitfinex can be one solution to invest our btc and both are market exchanges. i have invest my btc on there as lending and i can take profit on poloniex, but in bitfinex, i don't know.
while in gambling site, i am not yet trying to make invest my btc into any gambling sites, maybe later i will try.