Honestly though, if this limitation is not covered in their TOS, it's not something OP could have agreed to in anyway. It's very unreasonable to hold funds anyway, but to holw own funds under the limitations of a bonus scheme just absurd.
IMO if this wasn't in the TOS then the casino deserves to be shunned and perhaps even a scam report written against them for malpractice and attempting to extort BTC newbies.
IMO, if this is not in their TOS, Nitrogen would not hold the funds and require OP to do the rollover requirement. I am not sure if which part of the TOS since personally I am not reading all what is written every time I play in a certain site, just like a typical gambler I guess.
However on the part of OP since he is willing to deposit a huge amount, then he should know all the terms prior to depositing such amount.
Actually I agree with you, if OP seen that the site is scamming him, then probably a scam accusation is way better to get this problem notice easily.